Water treatment by dendrimer-enhanced filtration

ABSTRACT

Described herein are compositions and methods useful for the purification of water using dendritic macromolecules. The process involves using dendritic macromolecules (dendrimers) to bind to contaminants, and a filtration step to produce water from which contaminants have been removed or modified. Examples of dendrimers that may be used in the process include cation-binding dendrimers, anion-binding dendrimers, organic compound-binding dendrimers, redox-active dendrimers, biological compound-binding dendrimers, catalytic dendrimers, biocidal dendrimers, viral-binding dendrimers, multi-functional dendrimers, and combinations thereof. The process is readily scalable and provides many options for customization.

This application is a continuation of U.S. application Ser. No.11/182,314, entitled “WATER TREATMENT BY DENDRIMER-ENHANCED FILTRATION”,by Mamadou S. Diallo, which was filed on Jul. 15, 2005 now U.S. Pat. No.7,470,369, and which claims priority from U.S. Provisional ApplicationSer. No. 60/588,626, filed Jul. 16, 2004.

GOVERNMENT RIGHTS

The United States Government has certain rights in this inventionpursuant to Grant Nos. CTS-0086727 and CTS-0329436 awarded by theNational Science Foundation.

FIELD OF THE INVENTION

The invention relates to compositions and methods useful for removingcontaminants from water.

BACKGROUND OF THE INVENTION

Clean water is essential to human health. It is also a criticalfeedstock in a variety of key industries including the electronics,pharmaceutical and food industries. Treatment of groundwater, lakes andreservoirs is often required to make water safe for human consumption.For wastewater, treatment is necessary to remove harmful pollutants fromdomestic and industrial liquid waste so that it is safe to return to theenvironment. Current water treatment systems are generally large,centralized systems that comprise a number of steps, including treatmentwith anaerobic organisms, oxidizers, chlorine, and flocculants.

Because of their inherent flexibility, decentralized water treatmentsystems could provide more robust and cost effective means for dealingwith (i) declining sources of freshwater, (ii) more stringent waterquality standards and (iii) chemical and biological threats to localwater supplies. It has been proposed that distributed optimal technologynetworks (DOT-NET) are an alternative to the large, centralized watertreatment plants. The DOT-NET concept is predicated upon thedistribution and strategic placement of relatively small and highlyefficient treatment systems at specific locations in existing watersupply networks. Filtration processes that remove specific contaminantsare a key aspect of decentralized water treatment systems.

A number of water filtration processes have designed to remove organiccompounds and metal ions from contaminated wastes been described in theliterature. Two such processes are micellar-enhanced ultrafiltration(MEUF) (Scamehorn and Harwell, (1988) In Surfactant Based SeparationProcesses, Surfactant Science Series, Vol 33, Marcel Dekker, New York,Dunn et al., (1989) Coll. Surf 35:49, Baek et al., (2004) J. Haz. Mater.1081:19, Richardson et al., (1999) J. Appl. Polym. Sci. 4:2290) andpolymer supported ultrafiltration (PSUF) (Spivakov et al., (1985) Nature315:313, Geckeler et al., (1996) Envir. Sci. Technol, 30:725,Muslehiddinoglu et al., (1998) J. Memb. Sci, 140:251, Juang et al.,(1993) J. Membrane Sci. 82:163). In a typical MEUF process, a surfactantis added to polluted water. The aqueous solution is then passed throughan ultrafiltration membrane with pore sizes smaller than those of theorganic/metal ion laden micelles. In PEUF, a water-soluble linearpolymer with strong binding affinity for the target metal ions is addedto contaminated water. The resulting solution is passed through anultrafiltration membrane (UF) with pore sizes smaller than those of themetal ion-polymer complexes.

MEUF is based on the use of non-covalently bonded micelles to extractorganic solutes and/or bind metal ions. Micelles are dynamic andflexible structures with finite lifetime. Because of this, their size,shape, organic solubilization capacity, metal ion binding capacity andretention by UF membranes are very sensitive to surfactant concentrationand solution physical-chemical conditions (e.g., pH, temperature, ionicstrength, etc). Although the use of micellar solutions of heightmolecular weight block ABA copolymer of PEO-PPO-PEO surfactants couldreduce surfactant losses to a certain extent (Richardson et al., (1999)J. Appl. Polym. Sci. 4:2290), the leakage of surfactant monomers remainsa major problem in water treatment by MEUF.

In most cases, the surfactant solutions in MEUF processes are not veryselective and have relatively low organic solute and metal ion bindingcapacity. For the most part, they solubilize organic solutes throughpartitioning in their hydrophobic core and bind metal ions throughelectrostatic interactions with their charged head-groups. Moreover, thedevelopment of surfactant solutions with redox, catalytic and biocidalactivity remains a major challenge. Thus, MEUF has remained for the mostpart a separation process with limited practical applications.

The PSUF process has been primarily designed and evaluated to removemetal ions from contaminated wastewater streams. PSUF uses high molarmass linear polymers such as EDTA and macrocycles with amine groups(e.g., cyclams) that typically bind only one metal ion per molecule.While the components of a MEUF filtration system are somewhat adaptableto different functional groups, the PSUF process is not readilyfunctionalizable, and neither MEUF nor PSUF have been shown to becapable of catalytic reactions. Due to the ongoing demand for cleanwater and the limitations of the current methods, there is a significantneed in the art for a new water filtration process with a highercapacity for binding contaminants, as well as features that enable it tobe scalable, flexible, and configurable to suit a variety of differentwater purification needs.

SUMMARY OF THE INVENTION

The invention disclosed herein comprises a method of removingcontaminants from water. Embodiments of the invention include methods offiltering contaminated water, comprising providing a quantity ofcontaminated water, contacting the quantity of contaminated water withan amount of a dendrimer agent sufficient to bind at least a portion ofthe contaminants in the quantity of contaminated water to produce aquantity of contaminant-bound dendrimers, and filtering thecontaminant-bound dendrimers from the quantity of contaminated water,whereby a quantity of filtered water is produced.

Further embodiments provide methods wherein at least a portion ofdendrimers in the dendrimer agent remain unbound by contaminants, andfurther comprising filtering the unbound dendrimers from the quantity ofcontaminated water.

Still further embodiments involve filtering the contaminant-bounddendrimers, and comprise using a process selected from the groupconsisting of pressure, vacuum, gravity, and combinations thereof.

Other embodiments provide methods wherein filtering thecontaminant-bound dendrimers further includes using a filtration filterselected from the group consisting of nanofilters, ultrafilters,microfilters, and combinations thereof.

Other embodiments provide methods wherein the dendrimer agent comprisesa quantity of a tecto-dendrimer or a linear-dendritic copolymer.

Additional embodiments provide methods wherein the dendrimer agentcomprises a quantity of a dendrimer selected from the group consistingof cation-binding dendrimers, anion-binding dendrimers, organiccompound-binding dendrimers, redox-active dendrimers, biologicalcompound-binding dendrimers, catalytic dendrimers, biocidal dendrimers,viral-binding dendrimers, multi-functional dendrimers, and combinationsthereof.

Certain embodiments of the invention provide methods wherein thedendrimer is a cation-binding dendrimer that binds a metal that isselected from the group consisting of copper, cobalt, nickel, lead,cadmium, zinc, mercury, iron, chromium, silver, gold, cadmium, iron,palladium, platinum, gadolinium, uranium, arsenic, and combinationsthereof.

Other embodiments relate to methods wherein the contaminant-bounddendrimers are subjected to a recycling reaction to separate at least aportion of the contaminants from at least a portion of thecontaminant-bound dendrimers to produce a quantity of contaminants and aquantity of unbound dendrimers, and further comprising recycling thequantity of unbound dendrimers.

Another embodiment of the invention relates to a water filtrationsystem, comprising a reaction unit including a quantity of a dendrimeragent and a filtration unit in fluid communication with the reactionunit.

Other embodiments relate to a water filtration system wherein thefiltration unit comprises a filter selected from the group consisting ofnanofilters, ultrafilters, microfilters, and combinations thereof.

Still further embodiments pertain to a water filtration system whereinthe reaction unit and the filtration unit are integrated.

Additional embodiments of the invention relate to a water filtrationsystem wherein the dendrimer agent comprises a quantity of atecto-dendrimer or linear-dendritic copolymer.

Further embodiments relate to a water filtration system wherein thedendrimer agent comprises a quantity of a dendrimer selected from thegroup consisting of cation-binding dendrimers, anion-binding dendrimers,organic compound-binding dendrimers, redox-active dendrimers, biologicalcompound-binding dendrimers, catalytic dendrimers, biocidal dendrimers,viral-binding dendrimers, multi-functional dendrimers, and combinationsthereof.

Still further embodiments relate to a water filtration system comprisinga dendrimer recovery unit in fluid communication with the filtrationunit and configured to implement a recycling reaction to recycle aquantity of dendrimers.

Another embodiment relates to a water filtration system wherein thefiltration unit and the dendrimer recovery unit are integrated.

Certain embodiments of the invention relate to a method of bindingcontaminants in water, comprising providing a quantity of contaminatedwater, and contacting the contaminated water with a dendrimer agent.

Another embodiment relates to a method wherein the dendrimer agentcomprises a quantity of a dendrimer selected from the group consistingof tecto dendrimers, linear-dendritic copolymers, cation-bindingdendrimers, anion-binding dendrimers, organic compound-bindingdendrimers, redox-active dendrimers, biological compound-bindingdendrimers, catalytic dendrimers, biocidal dendrimers, viral-bindingdendrimers, multi-functional dendrimers, and combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sample embodiment of a dendrimer-enhanced filtrationsystem in accordance with an embodiment of the present invention.

FIG. 2 shows examples of different types of dendrimers in accordancewith an embodiment of the present invention.

FIG. 3 shows an example of a composite solid-supported filter forpurification of water contaminated by mixtures of cations, anions,organic/inorganic solutes, bacteria and viruses in accordance with anembodiment of the present invention.

FIG. 4 shows some examples of structures of PAMAM Dendrimers with EDACore and NH2 terminal groups in accordance with an embodiment of thepresent invention.

FIG. 5A shows the extent of binding of Cu(II) in aqueous solutions toEDA core G4-NH₂ PAMAM dendrimers as a function of metal ion dendrimerloading and solution pH in accordance with an embodiment of the presentinvention.

FIG. 5B shows the extent of binding of Cu(II) in aqueous solutions toG4-Ac(NHCOCH₃) PAMAM dendrimers as a function of metal ion dendrimerloading and solution pH in accordance with an embodiment of the presentinvention.

FIG. 6 shows a two-site model of Cu(II) uptake by G4-NH₂ PAMAM dendrimerin aqueous solutions in accordance with an embodiment of the presentinvention. The model fit was plotted against the measured extent ofbinding at room temperature and pH 7.0.

FIG. 7A shows the retention of EDA core G3-NH₂, G4-NH₂, and G5-NH₂ PAMAMdendrimers in aqueous solutions as a function of solution pH using aregenerated cellulose membrane in accordance with an embodiment of thepresent invention.

FIG. 7B shows the retention of EDA core G3-NH₂, G4-NH₂, and G5-NH₂ PAMAMdendrimers in aqueous solutions as a function of solution pH using apolyethersulfone membrane in accordance with an embodiment of thepresent invention.

FIG. 8A shows Cu(II) retention in aqueous solutions of EDA core G4-NH₂PAMAM dendrimers as a function of solution pH and molecular weightcut-off using a regenerated cellulose membrane in accordance with anembodiment of the present invention.

FIG. 8B shows Cu(II) retention in aqueous solutions of EDA core G4-NH₂PAMAM dendrimers as a function of solution pH and molecular weightcut-off using a polyethersulfone membrane in accordance with anembodiment of the present invention.

FIG. 8C shows Cu(II) retention in aqueous solutions of EDA core G3-NH₂,G4-NH₂, and G5-NH₂ PAMAM dendrimers as a function of dendrimer type andmembrane chemistry in accordance with an embodiment of the presentinvention.

FIG. 9A shows the permeate flux in aqueous solutions of Cu(II)+EDA CoreG4-NH2 PAMAM at pH 7, with a 10 kD cut-off regenerated cellulosemembrane in accordance with an embodiment of the present invention.

FIG. 9B shows the permeate flux in aqueous solutions of Cu(II)+EDA CoreG4-NH₂ PAMAM dendrimer as a function of solution pH and molecular weightcut-off with a regenerated cellulose membrane in accordance with anembodiment of the present invention.

FIG. 9C shows the permeate flux in aqueous solutions of Cu(II)+EDA CoreG4-NH₂ PAMAM dendrimer as a function of solution pH and molecular weightcut-off with a polyethersulfone membrane in accordance with anembodiment of the present invention.

FIG. 9D shows the permeate flux in aqueous solutions of Cu(II)+EDA CoreG3-NH₂, G4-NH₂, and G5-NH₂ PAMAM dendrimers at pH 7 with apolyethersulfone membrane, in accordance with an embodiment of thepresent invention.

FIG. 10A shows normalized permeate flux in aqueous solutions ofCu(II)+EDA core G4-NH₂ PAMAM dendrimer as a function of solution pH andmolecular weight cut-off with a regenerated cellulose membrane inaccordance with an embodiment of the present invention.

FIG. 10B shows normalized permeate flux in aqueous solutions ofCu(II)+EDA core G3-NH₂, G4-NH₂, and G5-NH₂ PAMAM dendrimers at pH 7 witha 10 kD molecular weight cut-off regenerated cellulose membrane inaccordance with an embodiment of the present invention.

FIG. 10C shows normalized permeate flux in aqueous solutions ofCu(II)+EDA core G4-NH₂ PAMAM dendrimers as a function of solution pH andmolecular weight cut-off with a polyethersulfone membrane in accordancewith an embodiment of the present invention.

FIG. 10D shows normalized permeate flux in aqueous solutions ofCu(II)+EDA core G3-NH₂, G4-NH₂, and G5-NH₂ PAMAM dendrimers at pH 7 witha 10 kD molecular weight cut-off polyethersulfone membrane in accordancewith an embodiment of the present invention.

FIG. 11A shows an AFM phase images of a clean regenerated cellulosemembrane in accordance with an embodiment of the present invention. Thescan area was 5 μm×5 μm. The image is of the 10 kD RC membrane asreceived.

FIG. 11B shows an AFM phase images a fouled regenerated cellulosemembrane in accordance with an embodiment of the present invention. Thescan area was 5 μm×5 μm. The 10 kD RC membrane was exposed to a 1.2310⁻⁵ mole/L aqueous solution of G4-NH₂ PAMAM dendrimer at pH 7.0.

FIG. 12A shows an AFM Phase image of a clean 10 kD polyethersulfonemembrane as received in accordance with an embodiment of the presentinvention. The scan area was 5 μm×5 μm.

FIG. 12B shows an AFM Phase image of a fouled 10 kD polyethersulfonemembrane that was exposed to a 1.23 10⁻⁵ mole/L aqueous solution ofG4-NH₂ PAMAM dendrimer at pH 7.0 in accordance with an embodiment of thepresent invention. The scan area was 5 μm×5 μm.

FIG. 13 shows the extent of binding of Co(II) in aqueous solutions ofEDA core G4-NH₂ PAMAM dendrimer at room temperature as function ofsolution pH and metal ion dendrimer loading in accordance with anembodiment of the present invention.

FIG. 14 shows the extent of binding of Ag(I) in aqueous solutions of EDAcore G4-NH₂ PAMAM dendrimer at room temperature as function of solutionpH and metal ion dendrimer loading in accordance with an embodiment ofthe present invention.

FIG. 15 shows the extent of binding of Fe(III) in aqueous solutions ofEDA core G4-NH₂ PAMAM dendrimer at room temperature as function ofsolution pH and metal ion dendrimer loading in accordance with anembodiment of the present invention.

FIG. 16 shows the extent of binding of Ni(II) in aqueous solutions ofEDA core G4-NH₂ PAMAM dendrimer at room temperature as function ofsolution pH and metal ion dendrimer loading in accordance with anembodiment of the present invention.

FIG. 17 shows the extent of binding of perchlorate in aqueous solutionsof G5-NH₂ DAB core PPI dendrimer in accordance with an embodiment of thepresent invention.

FIG. 18A shows the extent of binding of Fe(III) in aqueous solutions ofEDA core G4-NH₂ PAMAM dendrimer at room temperature and pH=7.0 inaccordance with an embodiment of the present invention.

FIG. 18B shows the fractional binding of Fe(III) in aqueous solutions ofEDA core G4-NH₂ PAMAM dendrimer at room temperature and pH=7.0 inaccordance with an embodiment of the present invention.

FIG. 19A shows the reductive dehalogenation of polychloroethylene inaqueous solutions of Fe(0) EDA core G4-NH₂ PAMAM dendrimernanocomposites in accordance with an embodiment of the presentinvention. The diamonds represent the amounts of polychloroethylene, andthe squares represent the amounts of tetrachloroethylene.

FIG. 19B shows the reductive dehalogenation of polychloroethylene inaqueous solutions with Fe(0) in the absence of EDA core G4-NH₂ PAMAMdendrimers, in accordance with an embodiment of the present invention.The diamonds represent the amounts of polychloroethylene, and thesquares represent the amounts of tetrachloroethylene.

DETAILED DESCRIPTION OF THE INVENTION

The invention disclosed herein relates to a novel process useful for theremoval of contaminants from water. The process, referred to as“dendrimer-enhanced filtration” (DEF) uses dendritic macromolecules, ordendrimers, and a filtration step to produce filtered water.

The DEF process, as shown in FIG. 1, is structured around three unitoperations: 1. a reaction unit; 2. a filtration unit, and 3. a dendrimerrecovery unit. In the reaction unit (103), contaminated water (102) ismixed with a solution of functionalized dendritic polymers (101) tocarry out any of a number of specific reactions of interest, includingmetal ion chelation, organic compound solubilization, contaminantoxidation-reduction, contaminant hydrolysis, binding of anions, andmicrobial/viral disinfection. Following completion of the binding of thecontaminants and/or the reaction, the resulting solution is passedthrough a filter in the filtration unit (105), producing a quantity oftreated water (106). A Pump, (104) or a plurality of pumps (not shown),may be used at a number of different stages of the process to promoteflow of the reaction components to various regions of the system. Thecontaminant laden dendrimer solutions are subsequently sent to anoptional dendrimer recovery unit (107), where the dendritic polymers,and if desired, the contaminants that were bound to the dendrimers(108), are recovered. The recycled dendrimers may be recycled back intothe reaction unit (109). The recovered contaminants may be otherwisedisposed of or utilized. The term “system” (100) refers to the overallDEF process, which may have any number or combination of some or all ofthe components described above or hereafter.

Dendrimers are a useful molecule for this purpose. Unlike micellarsurfactant solutions, aqueous solutions of dendritic polymers containcovalently globular nanostructures. Because of their polydispersity andpersistent globular shape over a broad range of solution pH andbackground electrolyte concentration, the leakage of dendritic polymersthrough filtration membranes with the appropriate molecular weightcut-off (MWCO) is highly improbable. Dendritic polymers also have muchless tendency to pass through filtration membranes than linear polymersof similar molar mass because of their much smaller polydispersity andglobular shape. Whereas the intrinsic viscosity of a linear polymerincreases with its molar mass, that of a dendrimer decreases as itadopts a molar globular shape at higher generations (Fréchet andTomalia, (2001) Dendrimers and other Dendritic Polymers; John Wiley andSons). Because of this, dendrimers have a much smaller intrinsicviscosity than linear polymers with similar molar mass. Thus,comparatively smaller operating pressure, energy consumption and loss ofligands by shear-induced mechanical breakdown can be achieved withdendrimers in tangential/cross-flow pressure driven filtration systemstypically used in water purification. Dendritic polymers can be designedto incorporate a wide variety of different functional groups thatfacilitate binding and/or reaction with a wide range of different typeof contaminants. Table 1 shows some examples of different types ofdendrimer reactive groups and their target contaminants; the list is byno means exhaustive.

TABLE 1 Dendrimer Active Groups, Target Contaminants, and RecyclingSystem Active Groups Target Contaminants Amines, Hydroxl, Carboxyl,TRIS, Succinamic Ag(I), Au(I) acid, Carbomethoxy pyrrolidinone, Oxalate,Cu(II), Ni(II) Imidazole, and other N, O, P and S containing Co(II),Pd(II), dendrimer terminal and internal groups. Pt(II), Mn(II) Fe(III),Co(III), Gd(III), U(VI), etc Transition metal ions, Redox active organicWater soluble organic an groups. Catalytic organic groups, etc.inorganic compounds, redox active metal ions, anions, organic andinorganic solutes, etc. Complexes with transition metal ions (Ag(I),Bacteria Cu(II), etc.), Bioactive organic groups Viruses, etc.Hydrophobic core Water soluble organic solutes Hydrophobic shell Alkylamines, Trialkyl amines, Amide NH Water soluble ions groups, Pyrrole NHgroups, Quaternary amoninum chlorides, Complexes with transition metalion (Cu(II)

The term “dendrimer”, or “dendritic macromolecule”, refers to 3-Dglobular macromolecules that may have three covalently bondedcomponents: a core, interior branch cells and terminal branch cells. Forthe purpose of this application, dendrimers include hyperbranchedpolymers, dendrigraft polymers, tecto-dendrimers,core-shell(tecto)dendrimers, hybrid linear-dendritic copolymers,dendronized polymers, dendrimer-based supramolecular assemblies anddendrimer-functionalized solid particles. FIG. 2 shows some examples ofdifferent types of dendrimers. They may be functionalized with surfacegroups that make them soluble in appropriate media or facilitate theirattachment to appropriate surfaces. They may be bioactive dendrimers, aslater defined herein.

The term “dendrimer agent” refers to a chemical composition containingdendrimers. The dendrimer agent may comprise a single dendrimer with asingle functionality, a single dendrimer with multiple functionalities,a mixture of dendrimers, dendrimers that have been cross-linked to otherdendrimers (tecto-dendrimers, or megamers), and dendrimers that havebeen covalently linked to polymers to produce linear-dendriticcopolymers or dendronized linear polymers.

A dendrimer agent may also include buffers, salts, stabilizers or inertingredients, and may be provided in a number of forms, including but notlimited to solids, solutions, suspensions, gels, semi-liquids, andslurries. As will be recognized by one of skill in the art, there is avariety of different dendrimer agent compositions that would be suitablefor the system and would therefore fall within the scope of the presentinvention.

A useful type of dendrimer is a poly(amidoamine) (PAMAM) dendrimer withan ethylene diamine (EDA) core. PAMAM dendrimers possess functionalnitrogen and amide groups arranged in regular “branched upon branched”patterns which are displayed in geometrically progressive numbers as afunction of generation level (FIG. 2). The high density of nitrogenligands enclosed within a nanoscale container makes PAMAM dendrimersparticularly attractive as high capacity chelating agents for metal ionsin aqueous solutions.

Commercially available PAMAM dendrimers may be used to developefficient, cost effective and environmentally-acceptable chelatingagents for removing arsenic, cadmium, chromium, copper, lead, mercuryand the toxic fluoride ion (F) from contaminated water. To this end,NH₂-terminated G3, G4 and G5 PAMAM dendrimers with an ethylene diamine(EDA) core may be reacted with the appropriate reagents to build PAMAMdendrimers with various terminal groups that are optimizable and havebinding specificities that target toxic metal ions and inorganiccontaminants. The dendrimer terminal groups may include hydroxide,acetamide, carboxylate, phosphonate, sulfonate and quaternary amine(methyl). In all cases, the chemical compositions of the surfacemodified dendrimers may be monitored by FTIR/¹³C NMR spectroscopy andsize exclusion chromatography. The molar masses of the surface modifiedPAMAM dendrimers may be determined by matrix assisted laser desorption(MALDI)-time of flight (TOF) mass spectrometry (MS) and gelelectrophoresis.

A system for carrying out the process of DEF may comprise a number ofdifferent components or units. The term “reaction unit” refers to acomponent of a water filtration system where dendrimers and contaminatedwater are mixed. The reaction unit may contain a single type ofdendrimer, or a mixture of different types of dendrimers, as well asmultifunctional dendrimers. In some cases, the dendrimers and thecontaminated water undergo a reaction, such as binding or catalysis, andthe reaction unit may be subjected to conditions that facilitate a sucha reaction. Such conditions include but are not limited to elevated orreduced temperature and elevated or reduced pH.

As used herein, the term “contaminated water” refers to water thatcontains a substance, or contaminant, that binds to or undergoes areaction catalyzed by a dendrimer. Possible substances include but areby no means limited to metal ions, anions, organic compounds, bacteria,viruses, and biological compounds such as proteins, carbohydrates, andnucleic acids. Contaminants are often toxic chemicals found in theenvironment that need to be removed from water in order to make itpotable. Examples of toxic compounds that may be removed or treated by aDEF system include copper, polychloroethelene, perchlorate, arsenate,chromium, and lead. The term “treated” or “filtered” water refers towater from which contaminants have been removed or catalyticallymodified.

The term “filtration unit” refers to a component of a water filtrationsystem wherein contaminated water that has been contacted with adendrimer agent is filtered such that water and free contaminants arefiltered out, but dendrimers and dendrimers with bound contaminants areretained on one side. It may also be referred to as a “clean waterrecovery unit”. The filter in the filtration unit is referred to as the“filtration unit filter”. The solution that passes through the membraneis referred to as the “filtrate”. The goal of the filtration unit is toproduce “clean” water; water from which a measurable, and in some casessubstantial amounts contaminants have been removed by the dendrimers. Itis within the scope of the application to have the reaction unitintegrated with the filtration unit. As used herein, the term“integrated” refers to multiple components that are mechanicallyinterconnected such as in a single physical unit.

The term “filter” refers to an entity that is often a physical barrier,that retains some molecules or compounds while allowing others to passthrough. In some cases, the selection of what passes through the filteris based on size; for example, a filter retains larger compounds andmolecules while allowing smaller ones to pass through. An example of asimple size-based filter is a porous membrane. Membrane based systemsmay be suitable for use in DEF, as a membrane may be used that has asmaller pore size than the dendrimers, so that dendrimers and dendrimerswith bound contaminants are retained by the membrane, while water fromwhich the contaminants have been removed passes through as a filtrate.

An alternative type of filter is one in which the filtering entity is incontact with a solid support or matrix. In this situation, dendrimersmay be attached to or deposited on a surface of a solid matrix. Forexample, with PAMAM dendrimers, the chemistry of the terminal groups maybe used to either covalently or non-covalently attach the dendrimers toa solid support. Contaminated water is provided to the dendrimer/matrixassembly, and binding of the contaminants to the dendrimer occurs. Waterfrom which at least a portion of the contaminants have been removed isproduced. Solid-supported filters may include a number of differentdendrimers and dendrimer types, including but in no way limited tocation/anion selective ligands, redox active metal ions and clusters,catalytically active metal ions and clusters, hydrophobic cavities, andbioactive agents. An example of a solid-supported filter is shown inFIG. 3.

Thus, the term “filter” encompasses but is not limited to membranes andsolid-support filters. It is also possible that a system has both amembrane filter and a solid supported filter in the same unit, or inseparate units operated in parallel or in series.

The filtration process, which separates the free dendrimers andcontaminant-bound dendrimers from the filtered water, may be driven bypressure, vacuum, or gravity. If pressure is used, it may be applied tothe side of the membrane containing the dendrimers to increase the flowof filtrate through the membrane. Pressure may be generated by theaddition of gas pressure, or may be mechanically applied. A vacuum maybe applied to the side of the membrane opposite of thedendrimer-containing side, to increase the flow rate from the other sideof the membrane. Filtration may also occur by simple gravity. Inaddition, combinations of pressure, vacuum, and gravity may be used.

Depending on the size and type of the dendrimers used in the system, thepore size of the filter may vary. Examples of different filter sizes areas follows: nanofilters, used for nanofiltration (NF), ultrafilters,used for ultrafiltration (UF), and micro filters, used formicrofiltration (MF). Nanofilters may have a pore size that is less thanabout 2 nanometers (nm) in diameter. Ultrafilters may have a pore sizeranging from about 2 to 20 nm, which may be useful for non-cross-linkeddendrimers. Microfilters may have membranes with pores larger than 20nm, which may be particularly useful for retaining cross-linkeddendrimers (tecto-dendrimers) or megamers. In general, the larger poresize of MF membranes allow a faster flow rates than the UF and NFmembranes.

The “dendrimer recovery unit” or “recycling unit” is a component of awater filtration system wherein at least a portion of the contaminantsthat were bound to dendrimers earlier in the process are then separatedfrom the dendrimers, producing a quantity of unbound dendrimers and aquantity of contaminant. Following removal of the contaminants from thedendrimers, the dendrimers may be re-used in future rounds of waterfiltration. Additionally, the contaminants may be recovered in therecycling process. In some circumstances, such as with valuable metalslike copper, recovery the “contaminants” may especially desirable.

The term “recycling reaction” refers to any process by whichcontaminant-bound dendrimers are recycled, recovered, regenerated, orotherwise returned to a state that is useful for binding contaminants.In cases where the binding capacity of the dendrimers exceeds the amountof contaminants in the solution, thereby leaving a portion of dendrimersun-bound following the reaction unit step, the un-bound dendrimers maybe subjected to a recycling reaction along with the contaminant-bounddendrimers. The type of recycling reaction used depends on the nature ofthe interaction between the contaminant and the dendrimer. Recyclingprocesses suitable for various dendrimer types are described below;although one of skill in the art will readily recognize a number ofvariations and additional processes that may be readily implemented, andare considered to be within the scope of the present invention. Therecycling reaction may take place in the dendrimer recovery unit, or inan integrated system, such as one where the filtration unit and thedendrimer recovery unit share the same membrane or filter.

In many cases, it is useful to formulate mixtures of dendritic polymerswith different functionalities to treat water contaminated bymulticomponent mixtures of chemical and biological contaminants. Incases where multi-component dendrimer agents are used, it may bedesirable to have multiple dendrimer recovery units, although this isnot required. If multiple dendrimer recovery units are used, they may beconfigured in series or in parallel.

In some cases, it may not be possible or desirable to recycle thedendrimers. For example, if the compounds that are bound in thedendrimers in the reaction unit are radioactive, or pose some other sortof environmental hazard, it may be desirable for the contaminant-bounddendrimers to be used only once.

It is also possible and well within the scope of the present inventionto have systems wherein the filtration unit and the dendrimer recoveryunit are integrated, or are a single unit. In the case of a membranefilter, a single membrane may used in both processes. In the case of asolid-support filter, the same unit may be subjected to differentconditions to promote either retention or recovery of contaminants.

There are many types of water treatment processes, and within thesetreatment processes, there are many stages where it is desirable toremove specific contaminants from water. The US Environmental ProtectionAgency is evaluating a number of alternative water purification systemsfor small communities (US EPA (1998) Office of Water Report EPA815-R-98-002). These include package treatment plants (i.e., factoryassembled compact and ready to use water treatment systems),point-of-entry (POE) and point-of-use (POU) treatment units designed toprocess small amounts of water entering a given unit (e.g., building,office, household, etc) or a specific tap/faucet within the unit. TheDEF processes and systems comprising the inventive DEF methods arereadily adaptable for these types of water treatment systems.

DEF processes and systems have the potential to be flexible,reconfigurable, and scalable. The process is scalable; it is limitedonly by very few factors (e.g., by the size of or number of filters ormembranes) as will be readily appreciated by those of skill in the art.The flexibility of DEF is illustrated by its adaptability to a modulardesign approach. DEF systems may be designed to be “hardware invariant”and thus reconfigurable in most cases by simply changing the dendrimeragent and dendrimer recovery system for the targeted contaminants. Thus,DEF may be used in small mobile membrane-based water treatment systemsas well as larger and fixed treatment systems and a host of othercommercial, residential, and industrial applications.

Dendrimer-enhanced filtration is a useful tool for removing cations fromaqueous solutions. More specifically, dendrimers may be used to formcomplexes with metal ions. Diallo et al. (Diallo, M. S. et al. (2005),Envir. Sci. Technol., 39: 1366-1377), have recently shown that DEF ismore effective than polymer-supported ultrafiltration (PSUF) atrecovering metal ions such as Cu(II) from contaminated water. In PSUF, awater-soluble linear polymer with strong binding affinity for the targetmetal ions is added to contaminated water [Geckeler, K. E and Volcheck.K. (1996), Envir. Sci. Technol., 30:725-734, Juang R. S. and Chen, M. N.(1997), Ind. Eng. Chem., 36: 179-186, Juang R. S. and Chiou, C. H.(2000), J. Membrane Sci., 177:207-214). The resulting solution is passedthrough an ultrafiltration membrane with pore sizes smaller than thoseof the metal ion-polymer complexes.

Metal ion complexation is an acid-base reaction that depends on severalparameters including (i) metal ion size and acidity, (ii) ligandbasicity and molecular architecture and (iii) solution physical-chemicalconditions. Three important aspects of coordination chemistry are theHard and Soft Acids and Bases (HSAB) principle, the chelate effect andthe macrocyclic effect (Martell and Hancock, (1996) Metal Complexes inAqueous Solutions; Plenum Press: New York). The HSAB principle provides“rules of thumb” for selecting an effective ligand (i.e., Lewis base)for a given metal ion (i.e., Lewis acid). Table 2 shows the bindingconstants of metal ions to selected unidendate ligands. The OH ligand isrepresentative of ligands with negatively charged “hard” 0 donors suchas carboxylate, phenolate, hydroxymate, etc (Martell and Hancock, (1996)Metal Complexes in Aqueous Solutions; Plenum Press: New York, Hancockand Martell (1996) J. Chem. Edu. 73:654). Conversely, NH₃ isrepresentative of ligands with “hard” saturated N donors (e.g. aliphaticamines); whereas imidazole is representative of “border line” hard/softligands with unsaturated N donors (Martell and Hancock, (1996) MetalComplexes in Aqueous Solutions; Plenum Press: New York). Themercaptoethanol group (HOCH₂CH₂S⁻), on the other hand, is representativeof ligands with “soft” S donors such as thiols (Martell and Hancock,(1996) Metal Complexes in Aqueous Solutions; Plenum Press: New York,Hancock and Martell (1996) J. Chem. Edu. 73:654).

TABLE 2 Binding Constants of Selected Metal Ions to Unidendate Ligandslog K₁ log K₁ log K₁ log K₁ Metal Ion (OH⁻) (NH₃) (Imidazole) HOCH₂CH₂S⁻Cu(II) 6.30 4.04 3.76 8.10 Co(II) 3.90 2.10 1.63 3.06 Ni(II) 4.10 2.701.92 3.14 Pb(II) 6.30 1.30 2.04 5.71 Cd(II) 3.9 2.55 2.54 7.45 Zn(II)5.00 2.21 1.86 3.19 Hg(II) 10.60 8.8 8.68 27.21 Fe(II) 3.60 1.4 1.412.9176 Fe(III) 11.81 3.8 3.51 8.5885 Cr(III) 10.07 3.40 3.05 7.3741Ag(I) 2.00 3.30 3.43 11.3369 Au(I) 2.70 5.6 5.63 18.769 Na(I) −0.20 −1.1−1.50 −4.72 Mg(II) 2.58 0.23 −0.01 −1.42 Ca(II) 1.30 −0.2 0.06 −0.07

Consistent with the HSAB principle, Table 2 shows that soft metal ionssuch Hg(II) and Au(I) tend to form more stable complexes with ligandscontaining S donors. Conversely, hard metal ions such Fe(III) tend toprefer hard ligands with 0 donors; whereas borderline hard/soft metalions such as Cu(II) can bind with soft/hard ligands containing N, 0 andS donors depending on their specific affinity toward the ligands.

The chelate effect is predicated upon the fact that metal ions formthermodynamically more stable complexes with ligands containing manydonor atoms than with unidentate ligands (Martell and Hancock, (1996)Metal Complexes in Aqueous Solutions; Plenum Press: New York).Conversely, the macrocyclic effect highlights the fact that metal ionstend to form thermodynamically more stable complexes with ligandscontaining preorganized cavities lined with donors (i.e., Lewis bases)than with multidendate and unidentate ligands (Martell and Hancock,(1996) Metal Complexes in Aqueous Solutions; Plenum Press: New York).

Dendritic macromolecules provide ligand architecture and coordinationchemistry for metal chelation. Although macrocycles and their “openchain” analogues (unidentate and polydentate ligands) have been shown toform stable complexes with a variety of metal ions (Martell and Hancock,(1996) Metal Complexes in Aqueous Solutions; Plenum Press: New York),their limited binding capacity (i.e. 1:1 complexes in most cases) is amajor impediment to their utilization as high capacity chelating agentsfor environmental separations such as water purification. Theirrelatively low molecular weights also preclude their effective recoveryfrom wastewater by low cost membrane-based techniques (e.g.,ultrafiltration and nanofiltration).

During the last 10 years, substantial research efforts have been devotedto the evaluation of the commercially available poly(amidoamine) (PAMAM)dendrimers from Dendritic Nanotechnologies (DNT) and Dendritech, and theASTRAMOL poly(propyleneimine) imines (PPI) dendrimers from DSM as (i)high capacity chelating agents, (ii) metal ion contrast agent carriersfor magnetic resonance imaging and (iii) templates for the synthesis ofmetal bearing nanoparticles with electronic, optical and catalyticactivity. These studies provide key data and insight into the selectionof water soluble and recyclable dendrimers with high binding capacityand selectivity toward a broad range of metal ions including Cu(II),Ni(II), Co(II), Pd(II), Pt(II), Zn(II), Fe(III), Co(III), Gd(III),U(VI), Ag(I), Au(I), etc.

Other commercially available dendritic polymers that could be used asmetal ion chelating agents include: 1. the water soluble phosphorousdendrimers available from Dendrichem and 2. the HYBRANE™ polyester amidehyperbranched polymers from DSM. Also applicable to the presentinvention is the recent development of a click chemistry route for thesynthesis of low cost Priostar dendrimers by DNT. According to DNT, thissynthetic method will allow “the introduction and control of sixcritical nanostructure design parameters that may be used to engineerover 50,000 different major variations of sizes, compositions, surfacefunctionalities and interior nanocontainer spaces that are expected tooffer new properties for use in a wide variety of commercialapplications”. In addition, Priostar dendrimers may provide a broadrange of low-cost and high capacity/selectivity recyclable dendriticchelating agents for water purification; they are suitable for use inconnection with alternate embodiments of the present invention and arethus considered to be within the scope thereof. Table 3 provides a listof some, but not all, commercially available dendritic polymers that maybe used as high capacity and recyclable chelating agents for waterpurification by dendrimer-enhanced filtration in accordance with variousembodiments of the present inventions.

TABLE 3 Commercially available dendritic polymers that may be used ashigh capacity and recyclable chelating agents for water purification bydendrimer enhanced filtration (DEF). Dendrimer Manufacturer ReactiveGroups Metal Ions PAMAM Dendritic Nano amines, hydroxyl, Ag(I), Au(I)Cu(II), dendrimers Technologies carboxyl, TRIS, Ni(II), Co(II), Pd(II),Dendritech succinamic acid, Pt(II), Mn(II) USA etc Fe(III), Co(III),Gd(III), U(VI), etc ASTRA- DSM amines, hydroxyl, Ag(I), Cu(II), Ni(II),MOL Netherlands carboxyl, etc Co(II), Fe(III), Gd(III), etc PriostarsDendritic Nano amines, hydroxyl, Ag(I), Au(I) Cu(II), DendrimersTechnologies carboxyl, ethers, Ni (II), Co(II), Pd(II), esters, thiol,Cd(II), Hg(II) Pt(II), imidazole, etc Zn(II) Fe(II), Pb(II), Fe(III),Co(III), Gd(III), Cr(III), Cr(VI), As(III), As(V), U(VI), etcPhosphorous Dendrichem Phosphate As(III), Hg(II) and Dendrimers FranceCd(II)

While a number of suitable recycling reactions may be effective atregenerating metal ion-binding dendrimers, certain embodiments compriseprotonating the dendrimer ligands by lowering the pH.

Dendrimer-enhanced filtration is a useful tool for removing organicsolutes from aqueous solutions. The release of anthropogenic organiccompounds (e.g., solvents, dyes, plastics, herbicides, pesticides andpharmaceuticals) into the environment is having a major impact on waterquality throughout the world (Schwarzenbach, et al. (2003),Environmental Organic Chemistry, 2d. Ed). Because micelles provide acompatible nanoenvironment for the partitioning of organic solutes,aqueous solutions of surfactants above their critical micelleconcentration (CMC) can significantly enhance the solubility of organicpollutants in water (Diallo, M. S. (1995), Solubilization of NonaqueousPhase Liquids and Their Mixtures In Micellar Solutions of EthoxylatedNonionic Surfactants, PhD Dissertation, University of Michigan, Pennel,K. D, et al. (1997), Environmental Science and Technology, 31:1382,Diallo, M. S., et al. (1994), Environmental Science and Technology,28:1829).

Several investigators have evaluated the utilization of micellarsurfactant solutions to remove organic pollutants from contaminatedgroundwater and industrial wastewater (Dunn, R. O., Jr., et al. (1985),Sep. Sci. Technol., 20:257-284, Purkait, M. K., et al., (2005), J.Membr. Sci., 250:47-59, Purkait, M. K., et al. (2005), J. Coll. Interf.Sci., 285:395-402). In a typical micellar enhanced ultrafiltration(MEUF) process, a surfactant or an amphiphilic block copolymer is addedto contaminated water (Dunn, R. O., Jr., et al. (1985), Sep. Sci.Technol., 20:257-284, Purkait, M. K., et al., (2005), J. Membr. Sci.,250:47-59, Purkait, M. K., et al. (2005), J. Coll. Interf Sci.,285:395-402). The resulting aqueous micellar solution is then passedthrough an ultrafiltration membrane with pore sizes smaller than thoseof the organic laden micelles.

Micelles are non covalently bonded aggregates; thus their solubilizationcapacity, size (i.e., aggregation number, micellar core volume, etc),shape (i.e., spherical versus cylindrical) and stability (i.e.,aggregation versus separation) depend to large extent on solutionphysicochemical conditions (e.g., surfactant concentration, temperature,pH, etc). Because micellization involves free energies of the order of10 RT (where R is the ideal gas constant and T is the solutiontemperature), micelles tend to be dynamic and flexible structures withfinite lifetime (Puvvada, S. and Blankschtein, D., (1990), J. Chem.Phys., 92:3710-3724, Israelachvili, J. N. (1992), Intermolecular andSurface Forces, 2^(nd) Ed). This makes their separation from aqueoussurfactant solutions by ultrafiltration much more challenging.

Dendritic macromolecules, on the other hand, can be designed andsynthesized as stable and covalently bonded micelle mimics that canencapsulate or binding organic solutes in aqueous and nonaqueoussolutions (Zeng F. and Zimmerman, S. (1997), Chem. Rev., 1681, Bosman,A. W., et al. (1999), Chem. Rev., 99:1665, Tomalia, D. A., et al. PNAS,99:5081-5087). Because of the persistent globular shape and lowpolydispersity, these micelle mimics can be easily separated fromaqueous solutions by UF, NF, MF.

Tomalia et al (Tomalia, D. A., et al. (1990), Angew. Chem., 102, 119)were among the first investigators to establish that dendriticmacromolecules such as PAMAM dendrimers can encapsulate organic solutes.They successfully combined ¹³C NMR relaxation measurements to show thatG4.5 (G4-COONa) and G5-NH2 PAMAM dendrimers can encapsulate organicmolecules such as acetylsalicyclic acid and 2,4-dichlorophenoxyaceticacid in chloroform. Pistolis et al. (Pistolis, G., et al. (1997),Langmuir, 13:5870) combined UV-VIS absorption and fluorescencespectroscopy to investigate pyrene solubilization in aqueous solutionsof GO, G1 and G2 PAMAM dendrimers. They found that the amount of pyrenesolubilized increases linearly with dendrimer generation. Watkins et al.(1997, Langmuir, 13:5870) have evaluated the interactions of red nile (aprobe that fluoresces intensely in hydrophobic lipids and organicsolvents) with a series of modified PAMAM dendrimers that were preparedby replacing their EDA core with diaminoalkanes. Their measurements ofthe probe fluorescence spectra in dilute aqueous solutions of themodified PAMAM dendrimers showed significant emission for dendrimerG3(C12) (i.e., generation 3 G3 with a C12 diaminoalkane core). Newkomeet al. (Newkome, G. R., et al. (1991), Angew. Chem., 30:1178) havesynthesized a dendrimer with an alkane core and 36 carboxyl terminalgroups that can bind hydrophobic probes such as phenol blue,7-chlorotetracycline and diphenylhexatriene in aqueous solutions. Hawkeret al. (Hawker, C. J., et al., (1993), J. Chem. Soc. Perkin. Trans.,1287) also reported the synthesis of a dendrimer with a polyaromaticether core and 32 carboxyl terminal groups that can solubilizehydrophobic organic compounds such as pyrene and 2, 3, 6,7-tetranitrofluorenone in aqueous solutions.

Dendritic macromolecules such as PAMAM dendrimers may also solubilizeorganic compounds through specific interactions with their amino groups.Kleinman et al. (Kleinman, M. H., et al. (2000), J. Phys. Chem., B104:11472-11479) have shown that 2-naphthol binds preferentially to thetertiary amine groups within the dendrimer interior. More recently,Caminade and Majoral (Caminade, A. M. and Majoral, J. P. (2005), Progr.Polym. Sci., 30:491-505) have described the preparation of water-solublephosphorous dendrimers that can bind organic solutes. These results showthat dendritic macromolecules may be used as micelle mimics that areuseful for recovering organic solutes from aqueous solutions bydendrimer enhanced filtration (DEF).

A number of different dendrimer agents may be suitable for use in a DEFsystem that is configured to remove organic solutes from aqueoussolution. Table 4 lists some manufacturers that produce dendrimers thatmay be used. Dendrimers that are useful in this system may have ahydrophobic core, or hydrophobic exterior, as well as a hydrophilic coreor a hydrophilic exterior. The uptake of organic solutes by dendriticmacromolecules in aqueous solutions may occur through several mechanismsincluding: 1. hydrophobic partitioning into the micellar core/shell, 2.hydrogen bonding to the macromolecule internal and terminal groups and3. specific interactions with the macromolecule internal and terminalgroups.

The recycling reaction for organic compound-binding may vary accordingto how the compounds are bound to the dendrimer. Some possible recyclingprocesses include but are not limited to 1) air stripping or vacuumextraction of the bound organic solutes, 2) pervaporation of the boundorganic solutes, 3) release of the bound organic solutes by protonationor deprotonation of the dendritic micelle mimics followed by OF or NFand 4) extraction of the bound organic solutes using a solvent,including “green” solvents such as ionic liquids

TABLE 4 Commercially available dendritic macromolecules that may be usedas dendritic micelle mimics for water purification by dendrimer enhancedfiltration (DEF). Macromolecule Manufacturer PAMAM dendrimers DendriticNano Technologies Dendritech USA ASTRAMOL DSM PPI dendrimers NetherlandsPAMAMOS-TMOS dendrimers Dendritech USA Priostar Dendrimers DendriticNano Technologies Phosphorous Dendrichem Dendrimers France HYBRANEHyperbranched Polymers DSM Netherlands BOLTORN Dendritic PolymersPerstop Sweden

Dendrimers in a dendrimer-enhanced filtration system may be used tofacilitate oxidations, reductions, or chemical transformations ofcontaminants in water. The contamination of groundwater by organic andinorganic pollutants has become a major problem in the US. In a studyconducted by the National Research Council, the number of sites withcontaminated groundwater has been estimated to range from 300,000 to400,000 (National Research Council (1997) Innovations in Groundwater andSoil Cleanup: From Concept to Commercialization. National Academy press,Washington D.C.). Pollutants in groundwater include chlorinated alkenessuch as perchloroethylene (PCE), poly(nitroaromatics) such as6-trinitrotoluene (TNT)) and redox active metal ions and anions such asCr(VI) and NO₃. However, most of these compounds may undergo reductive,oxidative and catalytic transformations in aqueous solutions.

Functionalized dendrimers that promote such transformations may be usedas reactive media for remediation of groundwater and surface watercontaminated by organic and inorganic solutes. Because of theirwell-defined size, shape and molecular composition, dendriticmacromolecules provide opportunities for developing a new generation ofredox active nanoparticles and catalysts for purification of watercontaminated by reactive organic and inorganic solutes. As used herein,the term “redox” refers to chemical reactions that involve loss of oneor more electrons by one molecule (oxidation) and simultaneous gain byanother (reduction).

A number of redox active dendritic catalysts have been synthesized andcharacterized that would be useful in a DEF water filtration system.These include dendrimers with ferrocene terminal groups that can oxidizeglucose or reduce nitrates (Astruc and Chardac, (2001) Chem. Rev.101:2991; Ooe, M et al. (2004). J. Am. Chem. Soc. 126: 604; Astruc, D etal. (2003). Macromolecular Symposia. 196: 1). Knapen et al. (1994)(Nature. 372: 659) have reported the preparation of carbosilanedendrimers with diaminoarylnickel(II) terminal groups, and have foundthat the Ni(II) functionalized dendrimers catalyze the Karsch additionof tetrachloromethane to methacrylate. Vassilev and Ford (1999) (J.Polym. Sci. Part A. 37: 2727) found that complexes of Cu(II), Zn(II) andCo(III) with poly(propyleneimine) dendrimers catalyze the hydrolysis ofp-nitrophenyl diphenyl phosphate (PNPDPP) in zwitterionic bufferedaqueous solutions. PNPDPP is often used as simulant for the chemicalwarfare agent such as Sarin. A number of dendritic catalytic systemshave also been successfully implemented in continuous membrane reactors(Astruc and Chardac, (2001) Chem. Rev. 101:2991).

In addition, several research groups have also exploited the uniqueproperties of dendrimers as nanoscale metal ion containers to synthesizemetal bearing nanoparticles with catalytic properties (Scott et al.(2005) J. Phys. Chem. B. 109:692; Esumi et al. (2004) Langmuir. 20:237).These nanoparticles, commonly referred to as dendrimer nanocomposites,can be efficiently prepared by reactive encapsulation, a process thatinvolves the complexation of guest metal ions followed by theirreduction and immobilization inside a dendritic host and/or at itssurface.

The inventor has shown the use of the Fe(0)/Fe(II) and Fe(II)/Fe(III)redox systems to develop water soluble and solid-supported dendriticnanoparticles to demonstrate the potential usefulness of dendrimernanocomposites and transition metal ion-dendrimer complexes in waterpurification The Fe(0)/Fe(II) and Fe(II)/Fe(III) redox couples can drivethe oxidative and reductive transformations of a variety oforganic/inorganic pollutants and toxic metal ions.

Reactions of relevance to water purification of water include: 1) thereductive dehalogenation of chlorinated hydrocarbons such PCE, 2) thereduction of Cr(VI) to Cr(III) and 3) the oxidation of As(III) to As(V)in the presence of dissolved oxygen. He initially focused on thereductive dehalogenation of PCE by Fe(0) dendrimer nanocomposites inaqueous solutions (Example 4 includes data on the reduction of PCE byFe(0) dendrimer nanocomposites).

The recycling reaction for redox active dendrimers may be accomplishedby a number of means, including electrochemical regeneration. In such areaction, the dendrimers may be placed in proximity to a an electrode,or redox couple that has a reduction potential that is favorable tooxidize or reduce the dendrimer catalyst to the state required forfurther rounds of catalysis. This may be accomplished in anelectrochemical cell, where an electrical current is applied, or byreacting the dendrimers with another redox-active metal. In cases wherethe dendrimers carry out other types of catalytic reactions, differenttypes of recycling processes may desirable, as will be readilyappreciated by those of skill in the art.

Persons of ordinary skill in the art would recognize that a number ofdifferent redox-active dendrimer agents would be suitable for use in thewater filtration system. A number of different commercial vendors mayprovide dendrimers with reactive groups including but not limited totransition metal ions, redox-active organic groups, and catalyticorganic groups. The target contaminants for such dendrimers include butare not limited to water soluble reactive organic and inorganiccompounds, redox active metal ions, anions, organic and inorganicsolutes. Table 4 lists some commercially available dendrimers that maybe used in the system.

The dendrimer-enhanced filtration process may be used to remove anionsfrom water. Anions have emerged as major water contaminants throughoutthe world because of their strong tendency to hydrate. In the US, thedischarge of anions such as perchlorate (ClO₄), pertechnetate (Tc)₄),chromate (CrO₄ ²⁻), arsenate (AsO₄ ³⁻), phosphate (HPO₄ ²⁻) and nitrate(NO₃) into publicly owned treatment works, surface water, groundwaterand coastal water systems is having a major impact on water quality.While significant research efforts have been devoted to the design andsynthesis of selective chelating agents for cation separations (Martell,A. E. and Hancock, R. D., Metal Complexes in Aqueous Solutions; PlenumPress: New York, 199, Hancock R. D. and Martell A. E. (1996), J. Chem.Edu., 73:654), anion separations have comparatively received limitedattention (Gloe, K., et al. (2003), Chem. Eng. Technol., 26:1107).

Unlike cations, anions have filled orbitals and thus cannot covalentlybind to ligands (Gloe, K., et al. (2003), Chem. Eng. Technol., 26:1107,Beer, P. D. and Gale, P. A. (2001), Angew. Chem. Int. Ed. Engl.,40:487). Anions have a variety of geometries (e.g., spherical for C1-and tetrahedral for C104) and are sensitive to solution pH in many cases(Gloe, K., et al. (2003), Chem. Eng. Technol, 26:1107, Beer, P. D. andGale, P. A. (2001), Angew. Chem. Int. Ed Engl., 40:487). Thus,shape-selective and pH-responsive receptors may be used to effectivelytarget anions. The charge-to-radius ratios of anions are also lower thanthose of cations (Gloe, K., et al. (2003), Chem. Eng. Technol, 26:1107,Beer, P. D. and Gale, P. A. (2001), Angew. Chem. Int. Ed Engl., 40:487).Thus, anion binding to ligands through electrostatic interactions tendsto be weaker than cation binding. Anion binding and selectivity alsodepend on (i) anion hydrophobicity and (ii) solvent polarity (Gloe, K.,et al. (2003), Chem. Eng. Technol., 26:1107, Beer, P. D. and Gale, P. A.(2001), Angew. Chem. Int. Ed. Engl., 40:487).

The instant application provides methods useful for removing anions fromwater. Dendrimers with reactive groups that promote anion bindinginclude but are not limited to alkyl amines, trialkyl amines, amide NHgroups, and pyrrole NH groups. Examples of anions that may be removed bya DEF process using anion-binding dendrimers include but are not limitedto ClO₄ ⁻, TcO₄ ⁻, CrO₄ ²⁻, AsO₄ ³, HPO₄ ², and NO₃ ⁻. An example of howperchlorate (ClO₄ ⁻) may be separated from water is shown in theExamples.

The recycling reaction for anions-binding dendrimers may comprisedeprotonating the dendrimer ligands by increasing the pH of the solutioncontaining the dendrimers. Table 4 shows some of the commerciallyavailable dendrimers that are suitable for as anion-selective ligandsfor water purification by dendrimer enhanced filtration.

Dendrimer-enhanced filtration may be useful for binding to and reactingwith biological entities such as bacteria and viruses, or subcellularcomponents of biological entities including but not limited to nucleicacids, proteins, carbohydrates, lipids, and drugs. Such dendrimers maybe referred to as “bioactive dendrimers”.

The removal and deactivation of microbial and viral pathogens arecritically needed to produce potable water. A variety of strong oxidants(e.g., chlorine and ozone) are used as disinfectants for pathogens(e.g., bacteria and viruses) in water treatment. Because these compoundstend to generate toxic disinfection byproducts such as trihalomethanes,haloacetic acids and aldehydes, alternative disinfectants are criticallyneeded to comply with the Stage 1 Disinfection Byproduct Rule 1996 ofthe Safe Drinking Water Act (SDWA) Amendments (USEPA (1998) FederalRegister. 63 (241): 69389). The mechanisms by which disinfectants suchas chlorine inactivate water borne pathogens include: (1) impairment ofpathogen cellular function by destruction of major constituents (e.g.,cell wall), (2) interference with the pathogen cellular metabolicprocesses, and (3) inhibition of pathogen growth by blockage of thesynthesis of key cellular constituents (e.g., DNA, coenzymes and cellwall proteins).

Because of their nanoscale size and high density of terminal groups,dendritic polymers provide useful platforms for targeting keybiochemical constituents of water borne bacteria and viruses. Bielinskaet al. (1997) (Biochem. Biophys. Acta. 1353:180) have reported that DNAand poly(amidoamine) PAMAM dendrimers form stable complexes throughelectrostatic interactions between negatively charged phosphate groupsof the nucleic acid and protonated (positively charged) amino groups ofthe polymer.

Dendritic polymers are readily conjugated to antibodies and thus havethe potential to target specific cells in vivo (Singh et al. (1994)Clin. Chem. 40:1845). They also offer non-toxic platforms for developingsynthetic inhibitors to viruses by blocking their adhesion to biologicalsubstrates. Comb-branched and dendrigraft polymers conjugated tomultiple sialic acid were evaluated for their ability to inhibit virushemagglutination and to block infection of mammalian cells in vitro(Reuter et al. (1999) Bioconjugate Chem. 10:271). The tested virusesincluded: 1. influenza A H2N2, 2. X-31 influenza A H3N2, and sendai. Themost effective virus inhibitors were the comb-branched and dendrigraftmacromolecules, which showed up to 50000-fold increased activity againstthese viruses.

Recently, the pharmaceutical company Starpharma announced the successfuldevelopment of a dendrimer-based biocide (VivaGel) that prevents HIVinfection by binding to receptors on the virus's surface (Halford (2005)Chem. & Eng. News 83 (24): 30). Chen at al. (2000) (Biomacromolecules.1:473) have reported that quaternary ammonium functionalizedpoly(propyleneimine) dendrimers are very potent biocides. Balogh et al.(2001) (Nano Letters. 1 (1): 18) have also shown that complexes of Ag(I)with PAMAM dendrimers and Ag(0)-PAMAM dendrimer nanocomposites displaybiocidal activity toward a wide range of bacteria includingStaphylococcus aureus, Pseudomonas aeruginosa, and Escherichia colibacteria.

Based on the research disclosed above, one of skill in the art wouldrecognize that there are a number of different dendrimer systems anddendrimer modifications that could be used to bind and/or inactivatebiological organisms or compounds. The recycling reaction for this typeof dendrimer would depend on the chemistry involved in the bindingbetween the dendrimer and the contaminant, but may include changes inpH, ionic strength, or reactions where the contaminant is competed awayfrom the dendrimer by another compound.

The following examples are offered by way of illustration and not by wayof limitation.

EXAMPLES Example 1 Recovery of Cu(II) from Aqueous Solutions Using PAMAMDendrimers with Ethylene Diamine Core and Terminal NH2 Groups

PAMAM dendrimers with ethylene diamine (EDA) core and terminal NH₂groups are synthesized via a two-step iterative reaction sequence thatproduces concentric shells of β-alanine units (commonly referred to asgenerations) around the central EDA initiator core (FIG. 4). Selectedphysicochemical properties of these dendrimers are given in Table 5.

TABLE 5 Selected Properties of EDA Core Gx-NH₂ PAMAM DendrimersEvaluated in this Study. ^(a)M_(wth) ^(f)R_(G) ^(g)R_(H) Dendrimer(Dalton) ^(b)N_(NT) ^(c)N_(NH2) ^(d)pK_(NT) ^(e)pK_(NH2) (nm) (NM)G3-NH₂ 6906 30 32 6.52 9.90 1.65 1.75 G4-NH₂ 14215 62 64 6.85 10.29 1.972.5 G5-NH₂ 28826 126 128 7.16 10.77 2.43 2.72 ^(a)M_(wth): Theoreticalmolecular weight. ^(b)N_(NT): Number of tertiary amine groups.^(c)N_(NH2): Number of primary amine groups. ^(d)pK_(NT): pKa ofdendrimer tertiary amine groups. ^(e)pK_(NH2): pKa of dendrimer primaryamine groups. ^(f)R_(G): dendrimer radius of gyration. For a dendriticpolymer with N atoms and molar mass M,${R_{G\;} = \left( {\frac{1}{m}\left\langle \left\lbrack {\sum\limits_{i = 1}^{N}\;{m_{i}{{r_{i} - R}}^{2}}} \right\rbrack \right\rangle} \right)^{0.5}};$where R, i the center-of-mass of the dendrimer and r_(i) and m_(i) arerespectively, the position and mass of atom i of the dendrimer (Maiti,P. K., (2004) Macromolecules, 32:6236-6254.). The R_(G) of the EDA CoreGx-NH₂PAMAM dendrimers were estimated from small angle neutronscattering experiments (Dvornic, P. R. et al., (2001) Dendrimers andother Dendritic Polymers; Fréchet, J. M. J., Tomalia, D. A., Eds.; Wileyand Sons: New York.). ^(g)R_(H): dendrimer hydrodynamic radius. It isusually estimated using Einstein's viscosity relation${R_{H} = \left( \frac{3\mspace{14mu}{\eta M}}{10\mspace{20mu}{\pi N}} \right)}\mspace{11mu}$(Armstrong, J. K. et al., (2004) Biophys. J. 87:4259-4270.); where M isthe molar mass of the particle/macromolecule, η is the intrinsicviscosity of its aqueous solution and N is Avogadro's number. The R_(H)of the EDA Core Gx-NH₂ PAMAM dendrimers were estimated from dilutesolution viscosity measurements (Dvornic, P. R. et al., (2001)Dendrimers and other Dendritic Polymers; Fréchet, J. M. J., Tomalia, D.A., Eds.; Wiley and Sons: New York.).

Diallo et al. (Diallo, M. S. et al., (2004) Langmuir, 20:2640-2651) haverecently carried out an extensive study of proton binding and Cu(II)complexation in aqueous solutions of EDA core PAMAM dendrimers ofdifferent generations (G3-NH₂, G4-NH₂ and G5-NH₂) and terminal groups(G4 PAMAM dendrimers with succinamic acid (NHCOCH₂CH₂COOH) terminalgroups, glycidyol (NHCH₂CH(OH)CH₂OH) terminal groups and acetamide(NHCOCH₃) terminal groups. This publication is incorporated herein byreference. In consistence with Tanford's theory of solute binding tomacromolecules (Tanford, C., (1961) Physical Chemistry ofMacromolecules; John Wiley & Sons: New York), they successfully used theextent of binding (EOB) to quantify Cu(II) uptake by the PAMAMdendrimers in aqueous solutions. The EOB of a metal ion in aqueoussolutions of a dendrimer is readily measured by (i) mixing andequilibrating aqueous solutions of metal ion+dendrimer, (ii) separatingthe metal ion laden dendrimers from the aqueous solutions byultrafiltration (UF) and (iii) and measuring the metal ionconcentrations of the equilibrated solutions and filtrates by atomicabsorption spectrophotometry (Diallo, M. S. et al., (1999) Environ. Sci.and Technol. 33:820-824-Diallo, M. S. et al., (2004) Langmuir,20:2640-2651). Table II compares the EOB of Cu(II) in aqueous solutionsof EDA core Gx-NH₂ PAMAM dendrimers to the Cu(II) binding capacity ofselected linear polymers with amine groups. On a mass basis, the EOB ofCu(II) to the Gx-NH₂ PAMAM dendrimers are much larger and more sensitiveto solution pH than those of linear polymers with amine groups that havebeen used in previous PEUF studies (Geckeler, (1996) Envir. Sci. Technol30, 725-734).

FIG. 5 provides evidence of the role of tertiary amine groups in theuptake of Cu(II) by EDA core PAMAM dendrimers in aqueous solutions. Boththe G4-NH₂ and G4-Ac EDA core PAMAM dendrimers have 62 tertiary aminegroups with pKa of 6.75-6.85. However, the G4-NH₂ PAMAM dendrimer has 64terminal groups with pKa of 10.20. Conversely, the G4-Ac PAMAM dendrimerhas 64 non ionizable terminal acetamide (NHCOCH₃) groups. At pH5.0, allthe primary and tertiary amine groups of PAMAM dendrimers becomeprotonated. FIG. 5 shows that no binding of Cu(II) occurs at pH 5 forboth the G4-NH₂ and G4-Ac PAMAM dendrimers. Conversely, significantbinding of Cu(II) is observed when a significant fraction or all of thedendrimer tertiary amine groups become unprotonated at pH 7.0 and 9.0.

To gain insight into metal ion coordination with the tertiary aminegroups of PAMAM dendrimers, Extended X-Ray Absorption Fine Structure(EXFAS) spectroscopy was employed to probe the structures of aqueouscomplexes of Cu(II) with EDA core Gx-NH₂ PAMAM dendrimers at pH 7.0.Analysis of the EXAFS spectra suggests the formation of octahedralcomplexes in which a Cu(II) central metal ion is coordinated to 4dendrimer tertiary amine groups and two axial water molecules inside thedendrimers.

To account for the Cu(II) ions that are not specifically bound to thedendrimers' tertiary amine groups at pH 7.0, it was hypothesized theformation of octahedral complexes of Cu(II) with water molecules trappedinside the Gx-NH₂ PAMAM dendrimers. A two-site thermodynamic model ofCu(II) binding to Gx-NH₂ PAMAM was subsequently formulated based on (i)the postulated mechanisms of Cu(II) coordination with the dendrimertertiary amine groups and bound water molecules, and (ii) Tanford'stheory of solute binding to macromolecules in aqueous solutions(Tanford, C., (1961) Physical Chemistry of Macromolecules; John Wiley &Sons: New York). This model expresses the EOB of Cu(II) in aqueoussolutions (at neutral pH) of Gx-NH₂ PAMAM dendrimers as function ofmetal ion-dendrimer loading (N_(Cu0)\T_(d)), number of dendrimertertiary amine group (N_(N) ^(d)), number of water molecules bound tothe dendrimers (NH_(2O-d)), metal ion amine group/bound watercoordination numbers (CN_(Cu(II)-N) ^(d) and CN_(Cu(II)-H2O)) ^(d)) andthe intrinsic association constants of Cu(II) to the dendrimer tertiaryamine groups and bound water molecules (k_(Cu(II)-N) ^(d) andk_(Cu(II)-H2O) ^(d)).

FIG. 6 highlights the results of a preliminary evaluation of the model.At low metal ion-dendrimer loadings, the model provides a good fit ofthe measured EOB of Cu(II) for the G4-NH₂ PAMAM dendrimer. The modelalso reproduces the increase in the EOB observed at higher metalion-dendrimer loadings following the first plateau. Note that thetwo-site model can also be used to estimate the binding constant of

${{Cu}({II})}\left\lbrack {K_{{{Cu}{({II})}} - N}^{d} = \frac{N_{N}^{d}}{k_{{{Cu}{({II})}} - N}^{d}}} \right\rbrack$to the tertiary amine groups of a Gx-NH₂ PAMAM dendrimer. TheK_(Cu(II)-N) ^(d) values for the G4-NH₂ and G5-NH₂ EDA core PAMAMdendrimers are respectively equal to 3.15 and 3.78. As shown in Table 7,the binding constants of Cu(II) to the tertiary amine groups of theGx-NH₂ PAMAM dendrimers (Diallo, M. S. et al., (2004) Langmuir,20:2640-2651) are comparable in magnitude to the formation constants ofCu(II)-ammonia complexes (Martell, A. E. et al., (1996), Metal Complexesin Aqueous Solutions; Plenum Press: New York). Ammonia (NH₃) isrepresentative of metal ion chelating agents with saturated N donors(Martell, A. E. et al., (1996), Metal Complexes in Aqueous Solutions;Plenum Press: New York). Table III also suggests that the Gx-NH₂ PAMAMdendrimers will selectively bind Cu(II) over first-row transition metalions such as Co(II) and Ni(II) and alkaline earth metal ions inwastewater such as Na(I), Ca(II) and Mg(II).

The dendrimer-enhanced filtration process (FIG. 1) is structured aroundtwo unit operations: 1. a clean water recovery unit and 2. a dendrimerrecovery unit. In the clean water recovery unit, contaminated water ismixed with a solution of functionalized dendritic polymers (e.g.,dendrimers, dendrigfrat polymers, hyperbranched polymers, core-shelltecto(dendrimers), etc) to carry out the specific reactions of interest(metal ion chelation in this case).

Following completion of the reaction, the resulting solution is filteredto recover the clean water. The contaminant laden dendrimer solutionsare subsequently sent to a second filtration unit to recover and recyclethe functionalized dendritic polymers (FIG. 1). As a proof-of-conceptstudy of this novel water treatment process, the inventor carried outdead-end ultrafiltration (UF) experiments to assess the feasibility ofusing DEUF to recover Cu(II) from aqueous solutions. To gain insightinto membrane fouling, he used atomic force microscopy (AFM) tocharacterize dendrimer sorption onto model UF membranes. The overallresults of these experiments suggest that DEUF is a useful process forrecovering Cu(II) from aqueous solutions.

The evaluation of the commercially available EDA core Gx-NH₂ PAMAMdendrimers (FIG. 4) was focused upon. G3-NH₂, G4-NH₂ and G5-NH₂ EDA corePAMAM dendrimers were purchased from Sigma-Aldrich and used as received.Selected physicochemical properties of the PAMAM dendrimers are given inTable 5. Cu(II) was selected as the model metal ion for this study.Reagent grade Cu(NO₃)₂ from Sigma-Aldrich was used as source of Cu(II).UF experiments were carried out to measure the retention of dendrimersand Cu(II)-dendrimer complexes by model UF membranes. The experimentswere performed in a 10-mL stirred cell (Amicon, Model 8010) with aneffective membrane area of 4.1 cm². A 1-gallon stainless steeldispensing pressure vessel (Millipore) was connected to the stirred cellusing PVC tubing. The reservoir was also equipped with a pressure gaugeand relief valve. Pressure from nitrogen gas was applied to the stirredcell via the reservoir at 450 kPa (65 psi). For each run, the initialvolume was 1 L. During each UF experiment, the stirred cell was operatedfor 4.5 hours with permeate collected every 30 minutes and fluxmeasurements taken every 10 minutes

Ultracel Amicon YM regenerated cellulose (RC) and PB Biomaxpolyethersulfone (PES) membranes from Millipore were evaluated in thisstudy. The RC and PES membranes had a diameter of 25 mm with molecularweight cut-off (MWCO) of 5000 Dalton (5 kD) and 10000 Dalton (10 kD).For the UF measurements of dendrimer retention in aqueous solutions, theconcentrations of the G3-NH₂ (2.42265 10⁻⁵ mole/L), 04-NH₂ (8.49762 10⁻⁶mole/L) and 05-NH₂ (5.31808 10⁻⁶ mole/L) PAMAM dendrimers were keptconstant in all experiments.

Dendrimer concentrations in the feed and permeate solutions weremeasured using a Shimadzu Model 1601 UV-Visible spectrophotometer atwavelength of 201 nm. A detailed description of analytical techniques(including HPLC with UV-Visible detection) used to characterize thecomposition and purity of EDA core PAMAM dendrimers is given in Diallo,M. S. et al., (2004) Langmuir, 20:2640-2651. For the UF measurements ofthe retention of metal ion-dendrimer complexes, a Cu(II) concentrationof 10 mg/L (0.00016 mole/L) was used in all experiments.

The molar ratio of Cu(II) to dendrimer NH2 groups was also kept constantat 0.2 in all experiments. The Cu(II)-dendrimer solutions weremaintained under constant agitation for 1 hour in the dispensingpressure vessel following adjustment of their pH with concentrated HClor NaOH. The pH of aqueous solutions of PAMAM dendrimers and theircomplexes with Cu(II) can be controlled within 0.1-0.2 pH unit byaddition of concentrated NaOH or HCl. The concentrations of metal ion inthe feed and permeate were determined by atomic absorptionspectrophotometry (Diallo, M. S. et al., (1999) Environ. Sci. andTechnol. 33:820-824-Diallo, M. S. et al., (2004) Langmuir,20:2640-2651). Solute retention (R) was expressed as:

$\begin{matrix}{R = {\left( {1 - \frac{C_{p}}{C_{f}}} \right) \times 100}} & (1)\end{matrix}$where C_(p) and C_(f) are, respectively, the concentration of solute[i.e., dendrimer and Cu(II)] in the permeate and feed. The permeate fluxJ_(p) (L h⁻¹ m⁻²) and normalized permeate flux (J_(pn)) were expressedas:

$\begin{matrix}{J_{p} = \frac{Q_{p}}{A_{UF}}} & (2) \\{J_{pn} = \frac{J_{p}}{J_{po}}} & (3)\end{matrix}$where Q_(p) is the permeate flow rate (L h⁻¹) and A_(UF) (m²) is theeffective area of the UF membrane and J_(po) (L h⁻¹ m⁻²) is the initialpermeate flux through the clean membranes.

Atomic force microscopy (AFM) was employed to characterize theinteractions of selected EDA core Gx-NH₂ PAMAM dendrimers and UFmembranes evaluated in this study. Each UF membrane was mounted on aperforated aluminum sheet and stored overnight in a desiccatorsfollowing exposure to a dendrimer aqueous solution as previouslydescribed. Tapping mode AFM experiments were carried out using a ModelDimension 3100 AFM from Digital Instruments. All AFM images wereacquired at room temperature using etched silicon probes with a springconstant of 20-100 N/m and a tip radius of 5-10 nm. The topographic andphase images of the clean and exposed UF membranes were acquiredsimultaneously using a probe resonance frequency of −300 kHz, a scanrate of 1 Hz, a free-oscillation amplitude (A_(o)) of 60 nm±5 nm and aset point to free amplitude ratio (rsp) of 0.50-0.75.

FIG. 7 highlights the effects of dendrimer generation and membranechemistry on the retention of EDA core Gx-NH₂ PAMAM dendrimers inaqueous solutions at pH 7.0 and room temperature. The retentions of theG5-NH₂ PAMAM dendrimer by the 10 kD regenerated cellulose (RC) andpolyethersulfone (PES) membrane are ≧97% in all cases. Such highretention values are expected for the G5-NH₂ EDA core PAMAM dendrimer, aglobular macromolecule with a low polydispersity and a molar mass of28826 Dalton (Table 5). Retentions greater than 90% were also observedfor the G4-NH₂ PAMAM dendrimer (FIG. 7). This dendrimer is also globularin shape and has very low polydispersity with a molar mass (14215Dalton) greater than the MWCO of the 10 kD RC and PES membranes (Table5). Possible explanations for the initial low retention (≈73%) of thisdendrimer by the 10 kD PES membrane include measurement errors and/orthe presence of impurities such as unreacted EDA and other lower molarmass reaction by-products in the 04-NH₂ PAMAM dendrimer sample (Diallo,M. S. et al., (2004) Langmuir, 20:2640-2651).

FIG. 7 also shows that the retentions of the G3-NH₂ EDA core PAMAMdendrimer are lower than those of the higher generation dendrimers. Thisdendrimer has the lowest molar mass (Table 5). For both membranes, thereis a significant retention of the G3-NH₂ dendrimer even though the MWCOof the dendrimers are 45% larger than the dendrimer molar mass (6906Dalton). In fact, the retention of the 03-NH₂ dendrimer by the 10 kD RCmembrane (FIG. 7) is comparable to that of a linear polyethyleneimine(PEI) polymer with an average molar mass of 50 to 60 kD (4). For UFmembranes, the MWCO is usually defined as the molar mass of a globularprotein with 90% retention.

Because dendritic polymers can be described as hybrids between polymerchains and colloidal particles (Harreis, H. M. et al., (2003) J. Chem.Phys. 118:1979-1988-Rathgeber, S. et al., (2002) J. Chem. Phys.117:4047-4062), the use of the MWCO as indicator of dendrimer retentionby UF membranes might not be adequate. Table 5 gives the radius ofgyration (RG) and hydrodynamic radius (R_(H)) of each EDA core Gx-NH₂PAMAM dendrimer evaluated in this study. R_(G) provides a measure of thesize of a particle/macromolecule regardless of its shape (Richards, E.G., (1980) An Introduction to Physical Properties of Large Molecules inSolution; IUPAB Biophysics Series, New York-Maiti, P. K., (2004)Macromolecules, 32:6236-6254). Conversely, R_(H) gives the size of an“equivalent” spherical particle/macromolecule (Armstrong, J. K. et al.,(2004) Biophys. J. 87:4259-4270). The R_(G) and R_(H) of the PAMAMdendrimers were, respectively, estimated from small angle neutronscattering experiments (Dvornic, P. R. et al., (2001) Dendrimers andother Dendritic Polymers; Fréchet, J. M. J., Tomalia, D. A., Eds.; Wileyand Sons: New York) and dilution solution viscosity measurements(Dvornic, P. R. et al., (2001) Dendrimers and other Dendritic Polymers;Fréchet, J. M. J., Tomalia, D. A., Eds.; Wiley and Sons: New York). Theyare comparable in magnitude to the mean pore surface diameters(1.93-3.14 nm) of a series of UF membranes (1-10 kD MWCO) that wasrecently characterized by Bowen and Doneva (Bowen, R. W., (2000) Surf.Interf. Analysis. 29:544-547). Whereas the molar mass of each Gx-NH₂PAMAM dendrimer increases by a factor of 2 at each generation, Table 5shows that the corresponding radii of gyration and hydrodynamic radiiincrease linearly with dendrimer generation. Table 5 also shows nosignificant differences between the R_(G) and R_(H) of each Gx-NH₂ PAMAMdendrimer. While not wishing to be bound by any particular theory, theinventor believes that the slightly higher R_(H) values could beattributed for the most part to dendrimer hydration. Because thedifferences in the retentions of the EDA core Gx-NH₂ PAMAM dendrimersare (for the most part) comparable to the differences between theirradii of gyration and hydrodynamic diameter, the R_(G)/R_(H) appears tobe a better indicator of dendrimer retention by UF membranes in aqueoussolutions.

The overall results of the measurements of dendrimer retention by the 10kD RC and PES membranes at pH 7.0 suggest that dendrimers such as theGx-NH₂ EDA core PAMAM have much less tendency to pass through the poresof UF membranes than linear polymers of similar molar mass because oftheir much smaller polydispersity and persistent globular shapes inaqueous solutions over a broad range of solution pH and backgroundelectrolyte concentration (Newkome, G. R. et al., (1996) DendriticMolecules. Concepts-Syntheses-Perspectives; VCH: New York; Fréchet, J.M. J. et al., (2001) Dendrimers and other Dendritic Polymers; Wiley andSons: New York; and Bosman, A. W. et al., (1999) Chem. Rev.99:1665-1668).

FIG. 8 highlights the effects of solution pH, membrane chemistry andMWCO on the retention of aqueous complexes of Cu(II) with a G4-NH₂ EDAcore PAMAM dendrimer at room temperature. A Cu(II) concentration of 10mg/L (0.00016 mole/L) was used in all experiments. The molar ratio ofCu(II) to dendrimer NH2 groups was also kept constant at 0.2 to ensurethat all the Cu(II) ions will be bound to the tertiary amine groups ofthe Gx-NH₂ PAMAM dendrimers at pH 7.0 (Diallo, M. S. et al., (2004)Langmuir, 20:2640-2651).

As shown in FIG. 8, 95 to 100% of the complexes of Cu(II) with theG4-NH₂ PAMAM dendrimer are retained by the RC membranes at pH 7.0. ThePES membranes also retain 92 to 100% of the Cu(II)-dendrimer complexesat pH 7.0. These results are consistent with the measurements ofdendrimer retention (FIG. 7) and metal ion binding measurements whichshow that 100% of the Cu(II) ions are bound to the G4-NH₂ PAMAMdendrimer at pH 7.0 and Cu(II) dendrimer terminal NH2 groups molar ratioof 0.2. Consistent with the results of the metal ion bindingmeasurements and dendrimer extent of protonation (Diallo, M. S. et al.,(2004) Langmuir, 20:2640-2651), no retention of Cu(II)-dendrimercomplexes by the RC membranes occurs at pH 4.0 (FIG. 8). However, asmall retention of Cu(II) (˜10%) is initially observed for both PESmembranes at pH 4.0. Possible explanations for this result includemeasurement errors and/or metal ion sorption onto the PES membranes.

FIG. 8 illustrates the effects of dendrimer generation on the retentionof Cu(II)-dendrimer complexes by the 10 kD membranes at pH 7.0. Hereagain, the observed retention values are consistent with the results ofthe dendrimer retention measurements (FIG. 7). Higher retention valuesare observed for the complexes of Cu(II) with the G5-NH₂ PAMAMdendrimer. Conversely, smaller retention values for the Cu(II)-dendrimercomplexes are observed with the G3-NH₂ PAMAM dendrimer (FIG. 8). Forboth membranes, FIG. 8 shows significant retentions of Cu(II) complexeswith the G3-NH₂ dendrimer (86-89% for the 10 kD RC membrane and 80-97%for the 10 kD PES membrane) even though the MWCO of each membrane is 45%larger than the dendrimer molar mass. These results also suggest thatthe MWCO of a UF membrane might not be an adequate indicator of theretention of Cu(II)+dendrimer complexes by UF membranes in aqueoussolutions.

Fouling is a major limiting factor to the use of membrane basedprocesses in environmental and industrial separations (Zeman, L. J. etal., (1996) Microfiltration and Ultrafiltration. Principles andApplications; Marcel Dekker: New York. and Kilduff, J. E. et al., (2002)Env. Eng. Sci. 19:477-495). A characteristic signature of membranefouling is a reduction in permeate flux through a membrane duringfiltration. The permeate fluxes of aqueous solutions of Cu(II) complexeswith Gx-NH₂ PAMAM dendrimers through RC and PES membranes at pH 7.0 and4.0 were measured. In these experiments, the Cu(II) concentration (10mg/L) and molar ratio of Cu(II) to dendrimer NH₂ groups (0.2) were alsokept constant. FIG. 9 shows the permeate fluxes through the RC and PESmembranes. For the 10 kD RC membrane at pH 7.0, the permeate flux showslittle change over the course of the filtration varying from 124.0 to116.0 L m⁻² h⁻¹. A similar behavior is also observed at pH 4.0. However,in this case, the permeate fluxes are approximately 16% higher. Thepermeate fluxes through the 5 kD RC membranes also exhibit littlevariation (49.0-43.0 L m⁻² h⁻¹) during the course of the filtration atpH 7.0 and 4.0 (FIG. 9). FIG. 9 also shows that dendrimer generationdoes not significantly affect the permeate flux through the 10 kD RCmembrane. This sharply contrasts the significant decline of permeateflux observed for the 5 kD and 10 kD PES membranes (FIG. 9). Althoughthe initial permeate fluxes are much larger for the PES membranes,significant flux declines (45 to 63%) occur during the filtration ofaqueous solutions of Cu(II) complexes with the G4-NH₂ PAMAM dendrimer atpH 7.0 and 4.0 (FIG. 9). In this case, we also observe a significantimpact of dendrimer generation on the permeate flux of aqueous solutionsof Cu(II)-dendrimer complexes through the 10 kD PES membranes at pH 7.0.FIG. 10 shows a decline in the normalized permeate fluxes for both theRC and PES membranes during the filtration of aqueous solutions ofCu(II) complexes with Gx-NH₂ PAMAM dendrimer at pH 7.0. For the 5 kD and10 kD RC membranes, a small decline in the relative permeate flux (7 to18%) is observed. However, the decrease in relative permeate flux (46 to81%) is much larger for the PES membranes. At pH 4.0, a significantdecrease in permeate flux (13 to 68%) is observed for the PES membranes.These results suggest that the PES membranes are more susceptible tofouling by the aqueous solutions of Gx-NH₂ PAMAM dendrimer+Cu(II) thanthe corresponding RC membranes.

The mechanisms of fouling of UF membranes are not well understood. Fororganic macromolecules such as proteins, linear polymers and humicacids, membrane fouling may be caused by (i) concentration polarizationresulting from solute accumulation near a membrane surface, (ii) poreblockage by solute sorption onto the surface of a membrane or within itspores and (iii) the formation of a cake layer by sorption/deposition ofsolutes on a membrane surface (Zeman, L. J. et al., (1996)Microfiltration and Ultrafiltration. Principles and Applications; MarcelDekker: New York. and Kilduff, J. E. et al., (2002) Env. Eng. Sci.19:477-495). To learn more about the fouling of the RC and PS membranesby EDA core Gx-NH₂ PAMAM dendrimers, the inventor used the data analysissoftware IGOR Pro Version 4.0 from WaveMetrics, Inc (IGOR Pro Version4.0. WaveMetrics) to fit the normalized permeate fluxes to twophenomenological models of membrane fouling (FIG. 7). The first model isa pore blockage model that expresses the decline in the normalizedpermeate flux as an exponential decay function (Zeman, L. J. et al.,(1996) Microfiltration and Ultrafiltration. Principles and Applications;Marcel Dekker: New York. and Kilduff, J. E. et al., (2002) Env. Eng.Sci. 19:477-495). This model did not provide a good fit of the data(results not shown). The second model expresses the decline in thenormalized permeate flux as a power-law function (Zeman, L. J. et al.,(1996) Microfiltration and Ultrafiltration. Principles and Applications;Marcel Dekker: New York. and Kilduff, J. E. et al., (2002) Env. Eng.Sci. 19:477-495):J _(pn)=(1+kt)^(−n)  (4)where k (h⁻¹) is a filtration rate constant and n is a dimensionlessexponent. As shown in FIG. 10 and Table 8, this model provides a verygood fit of the normalized permeate flux for the all the PES membranes.For the G4-NH₂ PAMAM dendrimer, the estimated values of n for the 10 kDPES membranes are 0.31±0.03 at pH 7.0 and 0.39±0.03 at pH 4.0 (Table 8).For the 5 kD PES membrane, the n values are equal to 0.36±0.02 at pH 7.0and 0.63±0.05 at pH 4.0 (Table 8). The n values for the G3-NH₂ andG5-NH₂ PAMAM dendrimers membranes are, respectively, equal to 0.45±0.05and 0.30±0.02 for the 10 kD PES membranes at pH 7.0. For dead-endultrafiltration, Zeeman and Zydney (Zeman, L. J. et al., (1996)Microfiltration and Ultrafiltration. Principles and Applications; MarcelDekker: New York) and Kilduff et al. (Kilduff, J. E. et al., (2002) Env.Eng. Sci. 19:477-495) have shown that the decline in permeate flux canbe described by a pore constriction model when n˜2. This model assumesthat the rate of change in the membrane pore volume is proportional tothe rate of particle convection to the membrane surface. When ˜0.5, thedecline in permeate flux in a dead-end ultrafiltration process can bedescribed by a cake filtration model (Zeman, L. J. et al., (1996)Microfiltration and Ultrafiltration. Principles and Applications; MarcelDekker: New York. and Kilduff, J. E. et al., (2002) Env. Eng. Sci.19:477-495). This model attributes the loss of permeate flux to particledeposition on the membrane surface. Based on the estimated n valuesgiven in Table 8, the sorption and deposition of dendrimer+Cu(II)complexes onto the membrane surfaces appears to be a plausible foulingmechanism for the PES membranes. We also believe that the small declinein the relative permeate fluxes (7 to 18%) through the 5K and 10 K RCmembranes (FIG. 10) could also be attributed to the sorption ofdendrimer-Cu(II) complexes onto the membrane surfaces.

TABLE 8 Fitted Model Parameters for the Normalized Permeate Flux ofAqueous Solutions of EDA Core Gx-NH₂ PAMAM Dendrimers + Cu(II) ThroughPolyethersulfone Membranes Membrane Dendrimer MWCO pH ^(a)k(h⁻¹) ^(a)n^(b)X² G4-NH₂ 10 kD 7.0 2.98 ± 0.58 0.31 ± 0.03 0.016 G4-NH₂ 10 kD 4.00.86 ± 0.13 0.39 ± 0.03 0.007 G4-NH₂  5 kD 7.0 0.62 ± 0.06 0.36 ± 0.020.001 G4-NH₂  5 kD 4.0 0.24 ± 0.05 0.63 ± 0.05 0.001 G5-NH₂ 10 kD 7.01.53 ± 0.21 0.30 ± 0.02 0.016 G3-NH₂ 10 kD 7.0 2.74 ± 0.75 0.45 ± 0.050.037 ^(a)k and n are determined by fitting the measured relativepermeate fluxes to Equation 4. ^(b)Goodness of fit parameter.${x^{2} = {\sum\limits_{i}\;\left( \frac{y - y_{i}}{\sigma_{i}} \right)}};$where y is the fitted value, y_(i) is the measured value and σ_(i) isthe estimated standard deviation for y_(i) (IGOR Pro Version 4.0.WaveMetrics).

To gain insight into the relationship between dendrimer sorption andmembrane fouling, the inventor used AFM to characterize RC and PESmembranes that have been exposed to a G4-NH₂ PAMAM dendrimer at pH 7.0during the filtration experiments. AFM has emerged as a powerful toolfor characterizing filtration membranes (Bowen, R. W., (2000) SurfInterf. Analysis. 29:544-547-Zeman, L. J. et al., (1996) Microfiltrationand Ultrafiltration. Principles and Applications; Marcel Dekker: NewYork; Khulbe, K. C. et al., (2000) Polymer. 41:1917-1935; Fritzsche, A.K., et al. (1992) J. Appl. Polym. Sci. 45:1945-1956; Zeng, Y. et al.,(2003) J. Appl. Polym. Sci. 88:1328-1335; Madaeni, S. S., (2004) J.Porous. Mat. 11:255-263; and Bowen, R. W. et al., (2002) Surf Interf.Analysis. 33:7-13). AFM has also successfully been used to characterizeGx-NH₂ PAMAM dendrimers adsorbed onto solid surfaces (Li, J. et al.,(2000) Langmuir. 16:5613-5616; Muller, T. M. et al., (2002) Langmuir.18:7452-7455; and Pericet-Camara, R. et al., (2004) Langmuir. 20:3264).FIGS. 12 and 13 show AFM phase images of clean and fouled 10 kD RC andPES membranes. A scan area of 5 μm×5 was used in all the AFMexperiments. The AFM images were subsequently analyzed (NanoscopeCommand Reference Manual; Software version 5.12, Revision B: DigitalInstruments/Veeco Metrology, 2001) to determine the roughness parameter(RMS), the mean roughness (R_(a)) and the maximum height (R_(max)) alongtwo different sections. The results of this analysis are given in Table9 and Supporting Information.

TABLE 9 Section Analysis of AFM Images of Clean and Fouled RegeneratedCellulose (RC) and Polyethersulfone (PES) Ultrafiltration Membranes.^(c)RMS ^(d)R_(a) ^(e)R_(max) Membrane Status nm nm nm 10 kD RC^(a)Clean 4.63-3.45 2.09-1.73 51.48-36.58 10 kD RC ^(b)Fouled 9.20-6.565.46-3.32 55.23-49.17 10 kD PES ^(a)Clean 14.96-13.07 11.76-9.28 51.75-47.56 10 kD PES ^(b)Fouled 14.07-14.22  9.90-10.25 61.66-65.86^(a)As received from Millipore. ^(b)Exposed to a 1.23 10⁻⁵ mole/Laqueous solution of G4-NH₂ PAMAM dendrimer in a 10-mL dead-end stirredcell (Amicon, Model 8010) during 4.5 hours.${\;^{c}{RMS}\mspace{14mu}{is}\mspace{14mu}{the}\mspace{14mu}{standard}\mspace{14mu}{deviation}\mspace{14mu}\sigma} = \sqrt{\frac{\sum\limits_{i}\;\left( {Z_{i} - Z_{ave}} \right)}{N}}$(Nanoscope Command Reference Manual; Software version 5.12, Revision B:Digital Intruments/Veeco Metrology, 2001.); where Z_(i) is the height atpoint i, Z_(ave) is the average height and N is the number of points ibetween the reference markers.${\;^{d}{Ra}\mspace{14mu}{is}\mspace{14mu}{the}\mspace{14mu}{{``{{Mean}\mspace{14mu}{Roughness}}"}.\mspace{14mu} R_{a}}} = {\frac{1}{L}{\int_{0}^{L}{{{f(x)}}\ {dx}}}}$(Nanoscope Command Reference Manual; Software version 5.12, Revision B:Digital Intruments/Veeco Metrology, 2001.); where L is the length of theroughness curve and f(x) is the roughness curve relative to the centerline. ^(e)R_(max) is the “Maximum Height” (Nanoscope Command ReferenceManual; Software version 5.12, Revision B: Digital IntrumentsNeecoMetrology, 2001.). It is the difference in height between the highestand lowest points on the cross sectional profile relative' to the centerline

Except for the presence of a few “rough” spots, the clean 10 kD RCmembrane exhibits a smooth and uniform skin. Conversely, the PESmembrane exhibits a dense, tightly, packed and grainy structurecharacteristics of membranes with nodular skin morphology (Zeman, L. J.et al., (1996) Microfiltration and Ultrafiltration. Principles andApplications; Marcel Dekker: New York). The RMS and R_(a) of the cleanPES membrane are significant larger than those of the clean RC membrane(Table 9). As shown in FIG. 11, only a small fraction of the fouled RCmembrane is covered by the sorbed G4-NH₂ PAMAM dendrimers. Most of thesorbed dendrimer molecules appear to cluster around the “rough” spots ofthe RC membrane surface (FIG. 11) thereby suggesting that dendrimersorption in this case is a non-specific process primary driven bymembrane surface roughness (Khulbe, K. C. et al., (2000) Polymer. 41:1917-1935. and Madaeni, S. S., (2004) J. Porous. Mat. 11:255-263). Thissharply contrasts the extensive coverage of the PES membrane surface bysorbed dendrimers (FIG. 12). While not wishing to be bound by anyparticular theory, the inventor believes that dendrimer sorption on thePES surface is mediated by electrostatic attractions between theprotonated terminal NH₂ groups of the G4-NH₂ PAMAM dendrimer (FIG. 6)and the negatively charged PES membranes at pH 7.0. The overall resultsof the AFM experiments suggest that there is a significant correlationbetween the extent of dendrimer sorption and membrane fouling.

Polymer enhanced ultrafiltration (PEUF) has emerged as a promisingprocess for recovering metal ions from aqueous solutions. The efficiencyof PEUF based processes for treatment of water contaminated by metalions will depend on several factors including: (i) polymer bindingcapacity and selectivity toward the targeted metal ions, (ii) polymermolar mass and responsiveness to stimuli such as solution pH, (iii)polymer sorption tendency onto OF membranes and (iv) polymer stabilityand toxicity. An ideal polymer for PEUF treatment of water contaminatedby metal ions should be highly soluble in water and have a high bindingcapacity/selectivity toward the targeted metal ions along with a lowsorption tendency toward OF membranes. Its molar mass should be highenough to ensure complete retention of the metal ion-polymer complexesby UF membranes without significant polymer leakage and decrease inpermeate flux. The metal ion binding capacity of an ideal polymer forPEUF should also exhibit sensitivity to stimuli such as solution pH overa range broad enough to allow efficient recovery and recycling of thepolymer by a simple change of solution pH. An ideal polymer for PEUFshould also be nontoxic and stable with a long life cycle to minimizepolymer consumption.

On a mass basis, the Cu(II) binding capacities of the Gx-NH₂ PAMAMdendrimers are much larger and more sensitive to solution pH (Table 6)than those of linear polymers with amine groups that have been used inprevious PEUF studies (Geckeler, (1996) Envir. Sci. Technol 30,725-734). Table 7 shows that Na(I), Ca(II) and Mg(II) have very lowbinding affinity toward ligands with N donors such as NH3. Thus, thehigh concentrations of Na(I), Ca(II) and Mg(II) found in most industrialwastewater streams are not expected to have a significant effect on theCu(II) binding capacity and selectivity of EDA core Gx-NH₂ PAMAMdendrimers.

TABLE 6 Cu(II) Binding Capacity (mg/g) of Gx-NH₂ EDA Core PAMAMDendrimers and Linear Polymers with Amine Groups in Aqueous SolutionsBinding Binding Binding Capacity Capacity Capacity Chelating Ligand pH =9.0 pH = 6-8.0 pH = 2.0-5.0 ^(a)G3-NH₂ PAMAM 420.0 333.0 (pH = 7.0) 0^(a)G4-NH₂ PAMAM 451.0 329.0 ± 8.0 (pH = 7.0) 0 ^(a)G5-NH₂ PAMAM 395.31308.0 ± 20.0 (pH = 7.0) 0 ^(b)Poly(ethyleneimine) NA 153.0 (pH = 6.0) 55(pH = 2.4)-189 (pH = 4.0) ^(b)Poly(ethylene) pyridine NA 120.0 (pH =6.0) NA 2-aldimine) ^(b)Poly(ethylene NA 120.0 (pH = 6.0) NAaminodiacetic acid ^(a)The Cu(II) binding capacity (mg/g) of the Gx-NH₂EDA core PAMAM dendrimers were estimated from their measured Cu(II)extents of binding (Diallo, M. S. et al., (2004) Langmuir, 20:2640-2651.). ^(b)The Cu(II) binding capacity of the linear polymers withamine groups were taken from Geckeler and Volchek (Geckeler, (1996)Envir. Sci. Technol 30, 725-734.).

TABLE 7 Formation Constants of Selected Metal Ion-Ammonia Complexes andEstimated Binding Constants of Cu(II) to the Tertiary Amines Groups ofEDA Core Gx-NH2 PAMAM Dendrimers ^(a)log K₁ ^(b)log K_(Cu(II)-N) ^(d)^(c)log K_(Cu(II)-N) ^(d) Metal Ion (NH₃) (G4-NH₂) (G4-NH₂) Cu(II) 4.043.15 3.78 Co(II) 2.10 ^(d)NA ^(d)NA Ni(II) 2.70 ^(d)NA ^(d)NA Na(I) −1.1^(d)NA ^(d)NA Mg(II) 0.23 ^(d)NA ^(d)NA Ca(II) −0.2 ^(d)NA ^(d)NA^(a)Data are taken from Martell and Hancock (Martell, A. E. et al.,(1996), Metal Complexes in Aqueous Solutions; Plenum Press: New York.).^(b)Estimated using the two-site thermodynamic model of Cu(II) bindingto Gx-NH₂ PAMAM dendrimers at neutral pH developed by Diallo et al.(Diallo, M. S. et al., (2004) Langmuir, 20: 2640-2651.).

As shown in FIG. 8, separation of the dendrimer-Cu(II) complexes fromsolutions can simply be achieved by ultrafiltration. The metal ionladen-dendrimers can also be regenerated by decreasing the solution pHto 4.0 (FIG. 8). Dendritic macromolecules such the Gx-NH₂ EDA core PAMAMdendrimers have also much less tendency to pass through the pores of UFmembranes (FIG. 7) than linear polymers of similar chemistry and molarmass (2, 4) because of their much smaller polydispersity and globularshape (Newkome, G. R. et al., (1996) Dendritic Molecules.Concepts-Syntheses-Perspectives; VCH: New York; Fréchet, J. M. J. etal., (2001) Dendrimers and other Dendritic Polymers; Wiley and Sons: NewYork; and Bosman, A. W. et al., (1999) Chem. Rev. 99:1665-1668). Theyhave also a very low tendency to foul the commercially availableregenerated cellulose (RC) membranes evaluated in this study (FIGS. 9,10, and 11). Whereas the intrinsic viscosity of a linear polymerincreases with its molar mass, that of a dendrimer decreases as itadopts a molar globular shape at higher generations (Fréchet, J. M. J.et al., (2001) Dendrimers and other Dendritic Polymers; Wiley and Sons:New York. and Bosman, A. W. et al., (1999) Chem. Rev. 99:1665-1668).Because of this, dendrimers have a much smaller intrinsic viscosity thanlinear polymers with similar molar mass (Fréchet, J. M. J. et al.,(2001) Dendrimers and other Dendritic Polymers; Wiley and Sons: NewYork. and Bosman, A. W. et al., (1999) Chem. Rev. 99:1665-1668). Thus,comparatively smaller operating pressure, energy consumption and loss ofligands by shear-induced mechanical breakdown could be achieved withdendrimers in tangential/cross-flow UF systems typically used to recovermetal ions from contaminated water (Geckeler, (1996) Envir. Sci. Technol30, 725-734). These unique properties of the Gx-NH₂ EDA core PAMAMdendrimers along with their low toxicity (Nanoscope Command ReferenceManual; Software version 5.12, Revision B: Digital Instruments/VeecoMetrology, 2001) make dendrimer-enhanced filtration (FIG. 1) aparticularly attractive process for recovering metal ions such as Cu(II)from contaminated water.

Example 2 Use of PAMAM Dendrimers for Binding to Additional Metals

Binding of Co(II), Ag(I), Fe(III), and Ni(II) to PAMAM dendrimers weretested at room temperature as a function of pH and metal ion dendrimerloading. The extent of binding for Co(II) is shown in FIG. 13. Theextent of binding for Ag(I) is shown in FIG. 14. The extent of bindingof Fe(III) is shown in FIG. 15. The extent of binding of Ni(II) is shownin FIG. 16.

Example 3

This example illustrates the use of dendrimer enhanced filtration (DEF)to recover anions from aqueous solutions, and focuses on the use ofdendritic ligands to bind perchlorate (ClO₄ ⁻). The dendrimers used werefifth generation (G5-NH₂) poly(propylene) (PPI) dendrimer with adiaminobutane (DAB) core and terminal NH2 groups. This is awater-soluble dendrimer with 64 terminal NH2 groups (pK_(a)=9.8) and 62internal tertiary amine groups (pK_(a)=6.0) with a theoretical molarmass of mass 7168 Dalton (10). The extent of binding (EOB) ofperchlorate to the DAB G5-NH₂ core PPI dendrimer were measured.

The binding assay procedure consisted of (i) mixing and equilibratingaqueous solutions of perchlorate and dendrimer at room temperature, (ii)separating the perchlorate-dendrimer complexes from the aqueoussolutions by ultrafiltration and (iii) measuring the concentration ofperchlorate in the equilibrated solutions and filtrates using a DionexDX-120 ion chromatograph with an IonPac AS16 analytical column and aIonPac AG16 guard column. FIG. 17 shows the EOB of perchlorate inaqueous solutions of the G5-NH₂ PPI dendrimer as a function ofanion-dendrimer loading and solution pH. In these experiments, we variedthe molar ratio of anion-dendrimer NH₂ group to prepare solutions with agiven perchlorate dendrimer loading. At pH 4.0, the terminal NH₂ groupsand tertiary amine groups of the PPI dendrimer are protonated. In thiscase, we observe significant binding of perchlorate up to 48 ClO₄ ⁻anions per mole of dendrimer.

On a mass basis, this corresponds to an EOB of 923 mg of perchlorate perg of dendrimer. This is approximately 9 times larger than the amount ofClO₄ ⁻ adsorbed (˜100 mg/g) after 24 hours onto the bifunctional ionexchange resins that are currently being used to treat watercontaminated by perchlorate (Moore, et al. (2003). Environ. Sci.Technol., 37:3189, Brown, et al. (2000) Perchlorate in the Environment.Edited by Urbansky, T. E. Kluver Academic, New York, pp 155-176). Notethe EOB of perchlorate in aqueous solution of the G5-NH₂ PPI dendrimerwas measured after an equilibration time of 30 minutes compared to 24hours for the ion exchange resin. While not wishing to be bound by anyparticular theory, the inventor believes that this fast binding kineticswill also be a key advantage of a homogenous liquid phase process suchas DEF. FIG. 17 shows significant binding of perchlorate to the G5-NH₂PPI dendrimer at pH 7.0 even though a significant fraction (>50%) of itstertiary amine groups (pK_(a)=6.0) are neutral (i.e., unprotonated).This suggests that the protonated terminal NH₂ (pK_(a)=9.8) groupsprovide a significant fraction of the electrostatic free energy ofperchlorate binding to the G5-NH₂ PPI dendrimer. Conversely, no bindingof perchlorate occurs at pH 11.0. In this case, all the tertiary andprimary tertiary are neutral. The overall results of these experimentsare consistent with the hypothesis that the (i) protonation of thetertiary and primary amine groups of the G5-NH₂ PPI dendrimer along with(ii) the hydrophobicity of its internal cavities will provide thedriving force for perchlorate binding and/or encapsulation in aqueoussolutions.

The results of these preliminary studies (FIG. 17) suggest that PPI andpoly(amidoamine) (PAMAM) dendrimers provide ideal building blocks forthe development of selective ligands for anions such as ClO₄—, CrO₄ ²⁻and HPO₄ ²⁻. Thus, it is expected that the replacement of the terminaland internal N groups of PPI and PAMAM dendrimers with alkyl amines,trialkyl amines and amide/pyrrole NH groups (Gale, P. A. (1999). Coord.Chem. Rev. 213:79-128) will provide a versatile synthetic route fordeveloping anion-selective dendritic ligands for water purification.These new ligands could be tuned to bind anions at low pH (˜3-5) whentheir N become protonated. Conversely, the bound anions could bereleased at higher pH (˜8-9) when the N groups of these dendrimersbecome neutralized. In fact this is a general ligand design strategythat could be applied to most dendritic macromolecules with ionizable Ngroups.

Example 4 Extent of Binding of Fe(III) in Aqueous Solution

Fe(0) (zero valent iron) nanocomposites were prepared by reduction ofaqueous complexes of Fe(III) with a generation 4 (G4-NH₂)polyamido(amine) (PAMAM) dendrimer with ethylene diamine (EDA) core andterminal NH₂ groups at pH 7.0. FIG. 18 shows the extent of binding andfractional binding of Fe(III) in aqueous solutions of G4-NH₂ EDA corePAMAM dendrimer at pH 7.0. Data were obtained using procedures shown byDiallo et al. (2004) Langmuir. 20:2640. These data indicate that most orall of the Fe is bound to the dendrimers.

Example 5 Synthesis of Zero Valent Iron PAMAM Dendrimer Nanocomposites

Redox-active Fe(0) PAMAM dendrimer nanocomposites were synthesized. Theoverall process involves adding Fe(III) to the interior of dendrimersand reducing the Fe(III) to Fe(0) with a reductant such as sodiumborohydrate, producing dendrimers having Fe(0) deposited inside. Theprocess leaves the surface groups of the dendrimers unmodified so thatthey can be used for other reactions, such as attachment to a solidsurface. In this case, the Fe(0) is used in a reductive dehalogenationreaction of polychloroethylene (PCE).

The synthesis of Fe(0) PAMAM dendrimer nanocomposites was carried in 8mL borosilicate glass vials at pH 7.0 by reacting 4 mL of aqueoussolutions Fe(II)-dendrimer complexes with excess sodium borohydrate(2000 ppm). The ability of the Fe(0) dendrimer nanocomposites (94 ppm ofFe(III) and molar ratio Fe(II)-NH2 0.125) to reduce the amounts PCE (10ppm) in aqueous solutions was evaluated using gas chromatography (GC)with electron capture detector (ECD) and flame ionization detector(FID).

The Fe(0)-containing nanocomposites are used to convert PCE totetrachloroethylene (TCE) (FIG. 19A). The control reaction (FIG. 19B)contains Fe(0) but no dendrimers. Preliminary investigations showedsignificant reduction of PCE (40-60% after 3 hours) by the Fe(0)-PAMAMdendrimer nanocomposites Conversely, only 20% of the 10 ppm of PCE wasreduced in aqueous solutions in the control Fe(0) particles synthesizedby reduction of 94 ppm Fe(III) with 2000 ppm of sodium borohydrate.

The results of these preliminary studies suggest that dendriticmacromolecules provide ideal building blocks for developing a newgeneration of generation of water soluble and solid-supported redoxactive nanoparticles and catalysts for water purification.

While the description above refers to particular embodiments of thepresent invention, it will be understood that many modifications may bemade without departing from the spirit thereof. The accompanying claimsare intended to cover such modifications as would fall within the truescope and spirit of the present invention. The presently disclosedembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims, rather than the foregoing description,and all changes that come within the meaning and range of equivalency ofthe claims are therefore intended to be embraced therein.

1. A method of filtering contaminated water, comprising: providing aquantity of water containing a quantity of a contaminant; contacting thequantity of water with an amount of a water soluble dendriticmacromolecules sufficient to bind at least a portion of the contaminantto produce a quantity of contaminant-bound dendritic macromolecules;filtering the quantity of contaminant-bound dendritic macromoleculesfrom the quantity of water, comprising the step of passing the waterthrough a first filtration membrane having pores or channels smallerthan the contaminant-bound dendritic macromolecules but larger than thecontaminant and larger than a water molecule, wherein thecontaminant-bound dendritic macromolecules are retained on the up-streamside of the first filtration membrane, whereby a quantity of filteredwater is produced; wherein the contaminant is selected from the groupconsisting of Co(II), Ag(I), Fe(III), Ni(II), ClO₄ ⁻, TcO₄ ⁻, and NO₃ ⁻;and wherein the dendritic macromolecule comprises: a core; a pluralityof arms extending from the core, the arms having a branched structureincluding a plurality of interior secondary branches; within theinterior secondary branches, a plurality of interior branch points, eachinterior branch point comprising an interior functional group includinga nitrogen or oxygen atom with a free electron pair capable of bindingwith a proton when the dendritic macromolecule is in an acidic aqueousenvironment; a plurality of terminal ends, each linked to an interiorsecondary branch; and zero valent iron embedded within the dendriticmacromolecule; wherein, when the dendritic macromolecule is placedwithin a first aqueous solution with a first pH between 1 and 11, andthe first aqueous solution is loaded with a mass of the contaminant ofabout one gram of contaminant per gram of dendritic macromolecule, theextent of binding is at least twice as great as when the dendriticmacromolecule is placed within a second aqueous solution with a secondpH between 1 and 11, and the second aqueous solution is loaded with themass of the contaminant.
 2. A method of filtering contaminated water,comprising: providing a quantity of water containing a quantity of acontaminant; contacting the quantity of water with an amount of adendritic macromolecule; and providing conditions whereby thecontaminant undergoes a catalytic or redox-active chemical reactioninvolving zero valent iron embedded within the dendritic macromolecule;wherein the dendritic macromolecule comprises: a core; a plurality ofarms extending from the core, the arms having a branched structureincluding a plurality of interior secondary branches; within theinterior secondary branches, a plurality of interior branch points, eachinterior branch point comprising an interior functional group includinga nitrogen or oxygen atom with a free electron pair capable of bindingwith a proton when the dendritic macromolecule is in an acidic aqueousenvironment; and a plurality of terminal ends, each linked to aninterior secondary branch; wherein the dendritic macromolecule is watersoluble.